day 24, interpreter working

I was overwriting created states in new-states while I should have been
cumulating.

05-hydrothermal-venture/code.scm

@@ -1,17 +1,5 @@
 (import (srfi :43)) ; vector extensions
-
-; returns numbers 0 to 9 from ascii character
-(define (char->number c)
-  (- (char->integer c) 48)) ; 48 is ASCII's number zero
-
-; reads a numnber from input
-; also consumes the next non-number character in the file!
-(define (get-number file)
-  (let loop [(n 0)]
-    (let [(c (get-char file))]
-      (if (char-numeric? c)
-	[loop (+ (char->number c) (* n 10))]
-	n))))
+(load "../common.scm")
 
 ; reads pairs of coordinates
 ; returns a list of the form (((x1 y1) (x2 y2))...)

09-smoke-basin/code.scm

@@ -1,39 +1,6 @@
 (import (srfi :43)) ; vector extensions
 (load "../common.scm")
 
-; constructor of heightmap object
-; from a vector of vector of altitudes
-(define (make-heightmap data)
-  (list
-    (vector-length (vector-ref data 0)) ; width
-    (vector-length data) ; height
-    data))
-
-; heightmap object getters
-(define (heightmap-width heightmap) (car heightmap))
-(define (heightmap-height heightmap) (cadr heightmap))
-(define (heightmap-data heightmap) (caddr heightmap))
-(define (sample-heightmap heightmap x y)
-  (if (or (< x 0)
-	  (< y 0)
-	  (>= x (heightmap-width heightmap))
-	  (>= y (heightmap-height heightmap)))
-    9
-    (vector-ref (vector-ref (heightmap-data heightmap) y) x)))
-
-; parse altitude data from file and return an heightmap object
-(define (load-heightmap file)
-  (let y-loop [(heightmap '())]
-    (let x-loop [(line '())]
-      (let [(c (get-char file))]
-	(cond
-	  [(eof-object? c)
-	   (make-heightmap (reverse-list->vector heightmap))]
-	  [(char-whitespace? c)
-	   (y-loop (cons (reverse-list->vector line) heightmap))]
-	  [(char-numeric? c)
-	   (x-loop (cons (char->number c) line))])))))
-
 ; constructor of low point objects
 ; from their position and altitude
 (define (make-low-point x y altitude)
@@ -50,17 +17,17 @@
       (lambda (y line)
 	(vector-for-each
 	  (lambda (x altitude)
-	    (let [(left (sample-heightmap heightmap (- x 1) y))
-		  (right (sample-heightmap heightmap (+ x 1) y))
-		  (up (sample-heightmap heightmap x (- y 1)))
-		  (down (sample-heightmap heightmap x (+ y 1)))]
+	    (let [(left (matrix-get heightmap (- x 1) y 9))
+		  (right (matrix-get heightmap (+ x 1) y 9))
+		  (up (matrix-get heightmap x (- y 1) 9))
+		  (down (matrix-get heightmap x (+ y 1) 9))]
 	      (when (and (< altitude left)
 			 (< altitude right)
 			 (< altitude up)
 			 (< altitude down))
 		(set! low-points (cons (make-low-point x y altitude) low-points)))))
 	  line))
-      (heightmap-data heightmap))
+      (matrix-data heightmap))
     low-points))
 
 ; compute risk level from low point list
@@ -70,8 +37,8 @@
 ; starting with from a given low-point
 ; call closure with and all points of the corresponding basin
 (define (visit-basin heightmap low-point closure)
-  (let* [(width (heightmap-width heightmap))
-	 (height (heightmap-height heightmap))
+  (let* [(width (matrix-width heightmap))
+	 (height (matrix-height heightmap))
 	 (width-1 (- width 1))
 	 (height-1 (- height 1))
 	 (visited (make-vector (* width height) 0))]
@@ -82,7 +49,7 @@
       (let [(ofs (offset x y))]
 	(when (= (vector-ref visited ofs) 0)
 	  (vector-set! visited ofs 1)
-	  (when (< (sample-heightmap heightmap x y) 9)
+	  (when (< (matrix-get heightmap x y 9) 9)
 	    (closure x y)
 	    (when (> x 0)        (flood-fill (- x 1) y))
 	    (when (< x width-1)  (flood-fill (+ x 1) y))
@@ -118,12 +85,12 @@
     (lambda (file)
       ; write header to file: "P3" followed by width, height and max value of channel
       (fprintf file "P3~%~a ~a~%255~%"
-	       (heightmap-width heightmap)
-	       (heightmap-height heightmap))
+	       (matrix-width heightmap)
+	       (matrix-height heightmap))
 
-      (let* [(width (heightmap-width heightmap))
+      (let* [(width (matrix-width heightmap))
 	     (width*3 (* width 3))
-	     (height (heightmap-height heightmap))
+	     (height (matrix-height heightmap))
 	     (data (make-vector (* width*3 width)))]
 
 	; from (x,y) returns of offset of pixel's red channel in data vector
@@ -136,7 +103,7 @@
 	(let y-loop [(y 0)]
 	  (let x-loop [(x 0)]
 	    (let [(ofs (offset x y))
-		  (gray-level (* (sample-heightmap heightmap x y) 20))]
+		  (gray-level (* (matrix-get heightmap x y 9) 20))]
 	      ; red channel
 	      (vector-set! data ofs gray-level)
 	      ; green channel
@@ -173,7 +140,7 @@
 (call-with-input-file
   "input"
   (lambda (file)
-    (let* [(heightmap (load-heightmap file))
+    (let* [(heightmap (load-matrix file))
 	   (low-points (find-low-points heightmap))]
       (printf "part 1:~% Risk level: ~a~%"
 	      (risk-level low-points))

10-syntax-scoring/code.scm

@@ -1,9 +1,4 @@
-; get list of lines from a file
-(define (get-lines file)
-  (let loop [(lines '())]
-    (if (eof-object? (peek-char file))
-      lines
-      (loop (cons (get-line file) lines)))))
+(load "../common.scm")
 
 ; check if character can close chunk
 (define (closing? c)

11-dumbo-octopus/code.scm

@@ -0,0 +1,72 @@
+(load "../common.scm")
+
+(define-record-type vec2i (fields x y))
+
+; flash given octopus
+; ie. increase energy of neighbor ones
+; returns list of octopuses that now need to flash too
+(define (flash! matrix x y)
+  (let [(extra '())]
+    (let y-loop [(yy (- y 1))]
+      (let x-loop [(xx (- x 1))]
+	(when (not (and (= xx x) (= yy y)))
+	  (when (< (matrix-get matrix xx yy 0) 10)
+	    (when (= (matrix-inc! matrix xx yy) 10)
+	      (set! extra (cons (make-vec2i xx yy) extra)))))
+	(when (< xx (+ x 1))
+	  (x-loop (+ xx 1))))
+      (when (< yy (+ y 1))
+	(y-loop (+ yy 1))))
+    extra))
+
+(define (step! matrix)
+  (let [(flashes '())]
+    ; increase energy of all octopuses
+    (update-matrix! 
+      matrix
+      (lambda (x y energy)
+	(when (= energy 9)
+	  (set! flashes (cons (make-vec2i x y) flashes)))
+	(+ 1 energy)))
+    ; recursively flash octopuses
+    (let loop [(flash flashes)]
+      (when (not (null? flash))
+	(loop (append (cdr flash)
+		      (flash! matrix (vec2i-x (car flash))
+			      (vec2i-y (car flash)))))))
+    ; drain all octopuses that flashed
+    (update-matrix! 
+      matrix
+      (lambda (x y energy)
+	(if (< energy 10) energy 0)))
+    ; count octopuses that flashed
+    (vector-fold
+      (lambda (y sum line)
+	(+ sum
+	   (vector-fold
+	     (lambda (x sum value)
+	       (if (= value 0) (+ sum 1) sum))
+	     0 line)))
+      0 (matrix-data matrix))))
+
+(call-with-input-file
+  "input"
+  (lambda (file)
+    (let [(matrix (load-matrix file))
+	  (flash-count 0)]
+      (let loop [(i 0)]
+	(set! flash-count (+ flash-count
+			     (step! matrix)))
+	(when (< i 99)
+	  (loop (+ i 1))))
+      (printf "part 1:~% ~a flashes after a hundred steps.~%"
+	      flash-count)
+      (let loop [(i 100)]
+	(if (= (matrix-sum matrix) 0)
+	  (printf "part 2:~% Octopuses synchronized at step ~a.~%" i)
+	  (begin
+	    (step! matrix)
+	    (loop (+ i 1))))))))
+
+
+

11-dumbo-octopus/input

@@ -0,0 +1,10 @@
+1326253315
+3427728113
+5751612542
+6543868322
+4422526221
+2234325647
+1773174887
+7281321674
+6562513118
+4824541522

12-passage-pathing/code.scm

@@ -0,0 +1,108 @@
+(load "../common.scm")
+
+; graphs in this code are represented by hashtables of node names to list of node names
+
+; splits string into two at first separator character encountered
+; returns #f if there is given separator is not present
+(define (split-string str separator)
+  (let [(len (string-length str))]
+    (let loop [(i 0)]
+      (if (= i len)
+	#f
+	(if (char=? (string-ref str i) separator)
+	  (list (substring str 0 i)
+		(substring str (+ i 1) len))
+	  (loop (+ i 1)))))))
+
+; add a directed edge to given graph
+(define (add-edge! nodes start end)
+  (hashtable-update! nodes start
+		     (lambda (node)
+		       (if (member end node)
+			 node
+			 (cons end node)))
+		     '()))
+
+; build graph from edges defined in a file
+(define (make-graph file)
+  (let [(lines (get-lines file))
+	(nodes (make-hashtable string-hash string=? 20))]
+    (for-each
+      (lambda (line)
+	(let [(edge (split-string line #\-))]
+	  (let [(start (car edge))
+		(end (cadr edge))]
+	    (add-edge! nodes start end)
+	    (add-edge! nodes end start))))
+      lines)
+    nodes))
+
+; big caves are uppercase nodes
+(define (is-big? node)
+  (char-upper-case? (string-ref node 0)))
+
+; count how many obj there is in lst
+(define (count-members obj lst)
+  (let count [(n 0) (lst lst)]
+    (let [(sub (member obj lst))]
+      (if sub
+	(count (+ n 1) (cdr sub))
+	n))))
+
+; calls visitor for all possible paths in graph
+; with max-small = 1, visits small caves at most once
+; with max-small = 2, visits one small cave at most twice and others at most once
+; with max-small >= 3 or 0, probably garbage
+(define (visit-paths graph max-small visitor)
+  (let visit [(node "start")
+	      (path '())
+	      (max-small max-small)]
+    (if (string=? node "end")
+      (visitor (cons node path))
+      (for-each
+	(lambda (child)
+	  (let [(is-big (is-big? child))]
+	    (when (and (not (string=? child "start"))
+		       (or is-big
+			   (< (count-members child path) max-small)))
+	      (visit child (cons node path)
+		     (if (and (not is-big) (member child path)) 1 max-small)))))
+	(hashtable-ref graph node '())))))
+
+; computes how many possible paths there are in graph
+(define (count-paths graph max-small)
+  (let [(count 0)]
+    (visit-paths graph max-small
+		 (lambda (path)
+		   (set! count (+ 1 count))))
+    count))
+
+; print all possible paths
+(define (print-paths graph max-small)
+  (visit-paths graph max-small
+	       (lambda (path)
+		 (printf "~a~%" (reverse path)))))
+
+;(let [(nodes (make-hashtable string-hash string=? 20))]
+;  (define (add-2! s e)
+;    (add-edge! nodes s e)
+;    (add-edge! nodes e s))
+;  (add-2! "start" "A")
+;  (add-2! "start" "b")
+;  (add-2! "A" "c")
+;  (add-2! "A" "b")
+;  (add-2! "b" "d")
+;  (add-2! "A" "end")
+;  (add-2! "b" "end")
+;  (printf "~a of them at 1 small~%" (count-paths nodes 1))
+;  (printf "~a of them at one 2 small~%" (count-paths nodes 2))
+;  (print-paths nodes 2))
+
+(call-with-input-file
+  "input"
+  (lambda (file)
+    (let [(graph (make-graph file))]
+      (printf "part 1:~% ~a paths with at most 1 visit to small caves.~%"
+	      (count-paths graph 1))
+      (printf "part 2:~% ~a paths with at most 2 visits to small caves.~%"
+	      (count-paths graph 2)))))

12-passage-pathing/input

@@ -0,0 +1,22 @@
+zi-end
+XR-start
+zk-zi
+TS-zk
+zw-vl
+zk-zw
+end-po
+ws-zw
+TS-ws
+po-TS
+po-YH
+po-xk
+zi-ws
+zk-end
+zi-XR
+XR-zk
+vl-TS
+start-zw
+vl-start
+XR-zw
+XR-vl
+XR-ws

13-transparent-origami/code.scm

@@ -0,0 +1,69 @@
+(load "../common.scm")
+
+; reads a number from file up until the first non numeric character
+(define (read-number file)
+  (let loop [(n 0)]
+    (let [(c (get-char file))]
+      (if (or (eof-object? c)
+	      (not (char-numeric? c)))
+	n
+	(loop (+ (* n 10)
+		 (char->number c)))))))
+
+; parses pairs of numbers separated by one character
+(define (read-coords file)
+  (let loop [(coords '())]
+    (if (char-numeric? (peek-char file))
+      (loop (cons (list (read-number file)
+			(read-number file))
+		  coords))
+      coords)))
+
+; parses lines of "fold along A=N" where A is a character or N is a number
+(define (read-folds file)
+  (let loop [(folds '())]
+    (if (eof-object? (peek-char file))
+      (reverse folds)
+      (begin
+	(get-string-n file 11) ; consume "fold along "
+	(let [(axis (get-char file))
+	      (position (begin
+			  (get-char file) ; consume =
+			  (read-number file)))]
+	  (loop (cons (list axis position) folds)))))))
+
+; mirrors coordinates along given axis and line/column
+; returns a new list of coordinates
+(define (fold coords axis-position)
+  (let-values [((axis position) (apply values axis-position))]
+    (let* [(position*2 (* position 2))
+	   (mirror (if (char=? axis #\x)
+		     (lambda (x y) (list (if (> x position) (- position*2 x) x) y))
+		     (lambda (x y) (list x (if (> y position) (- position*2 y) y)))))
+	   (transform (lambda (output coord)
+			(let [(mirrored (apply mirror coord))]
+			  (if (member mirrored output) output (cons mirrored output)))))]
+      (fold-left transform '() coords))))
+
+(call-with-input-file
+  "input"
+  (lambda (file)
+    (let* [(coords (read-coords file))
+	   (folds (begin
+		    (get-char file) ; consume newline
+		    (read-folds file)))]
+      (let [(first-fold (fold coords (car folds)))]
+	(printf "part 1:~% ~a dots after first fold.~%"
+		(length first-fold)))
+      (let [(fully-folded (fold-left fold coords folds))]
+	(let [(width (+ 1 (fold-left (lambda (m c) (max m (car c))) 0 fully-folded)))
+	      (height (+ 1 (fold-left (lambda (m c) (max m (cadr c))) 0 fully-folded)))]
+	  (printf "part 2:~% Code is:~%")
+	  (let y-loop [(y 0)]
+	    (when (< y height)
+	      (let x-loop [(x 0)]
+		(when (< x width)
+		  (printf (if (member (list x y) fully-folded) "#" " "))
+		  (x-loop (+ x 1))))
+	      (printf "~%")
+	      (y-loop (+ y 1)))))))))

13-transparent-origami/input

@@ -0,0 +1,789 @@
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+1027,714
+1101,320
+182,474
+801,767
+1260,381
+72,253
+195,73
+390,497
+1056,508
+107,275
+753,504
+699,180
+890,540
+894,105
+509,270
+530,249
+378,94
+50,65
+870,486
+1029,667
+728,840
+974,809
+803,751
+92,354
+749,509
+1198,206
+144,0
+290,208
+1195,249
+470,647
+1233,809
+801,270
+874,793
+903,406
+310,192
+1109,551
+806,812
+1069,841
+1161,158
+1044,311
+1168,23
+542,227
+1268,361
+1166,446
+421,385
+782,432
+478,82
+1034,885
+1154,217
+216,859
+677,497
+372,660
+806,82
+612,704
+483,201
+820,260
+933,418
+873,885
+744,789
+147,143
+594,220
+45,144
+1268,135
+699,119
+383,221
+27,854
+328,352
+499,880
+1298,75
+437,317
+102,52
+1184,432
+996,826
+448,25
+1211,764
+987,165
+913,133
+35,595
+271,436
+1036,155
+1255,624
+1287,690
+1298,714
+492,688
+827,693
+1129,521
+1028,196
+1176,388
+654,190
+967,106
+340,364
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+59,670
+495,606
+768,227
+576,873
+746,844
+618,82
+1238,253
+387,84
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+631,690
+705,418
+937,711
+1207,152
+152,682
+768,829
+528,686
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+1183,141
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+35,487
+44,749
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+326,816
+1251,224
+1310,381
+1109,343
+1211,255
+60,138
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+1290,838
+534,645
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+1074,50
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+209,768
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+512,838
+316,212
+820,16
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+985,691
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+811,880
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+344,416
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+769,871
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+1039,436
+1033,812
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+517,337
+582,844
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+92,281
+671,655
+550,565
+125,103
+699,404
+228,752
+1298,371
+576,649
+552,380
+1260,513
+821,427
+783,141
+0,78
+683,40
+806,826
+552,276
+371,567
+431,0
+267,532
+1086,808
+336,278
+372,234
+530,46
+58,628
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+855,546
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+242,537
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+1201,129
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+1183,779
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+59,224
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+865,320
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+975,649
+490,260
+545,577
+156,5
+383,669
+913,532
+119,164
+162,688
+1092,793
+
+fold along x=655
+fold along y=447
+fold along x=327
+fold along y=223
+fold along x=163
+fold along y=111
+fold along x=81
+fold along y=55
+fold along x=40
+fold along y=27
+fold along y=13
+fold along y=6

14-extended-polymerization/code.scm

@@ -0,0 +1,124 @@
+(import (srfi :43)) ; vector extensions
+
+; hash function for a list of two characters
+(define (char-pair-hash cp)
+  (+ (* (char->integer (car cp)) 79)
+     (char->integer (cadr cp))))
+
+; parses lines of "AB -> C" with A, B and C being characters
+; returns hashtable where keys are ABs and values are Cs
+(define (read-table file)
+  (let loop [(table (make-hashtable char-pair-hash equal? 32))]
+    (let [(line (get-line file))]
+      (if (eof-object? line)
+	table
+	(let [(key (list (string-ref line 0) (string-ref line 1)))
+	      (value (string-ref line 6))]
+	  (hashtable-set! table key value)
+	  (loop table))))))
+
+; generate new polymer from inserting elements in between each pair according to given table
+(define (insert polymer table)
+  (let [(end (- (string-length polymer) 1))]
+    (let loop [(i 0) (output "")]
+      (if (< i end)
+	(loop (+ i 1)
+	      (let* [(pair (list (string-ref polymer i) (string-ref polymer (+ i 1))))
+		     (element (hashtable-ref table pair #f))]
+		(if element
+		  (string-append output (string (car pair)) (string element))
+		  (string-append output (string (car pair))))))
+	(string-append output (substring polymer end (+ end 1)))))))
+
+; parameter counts is a vector where each entry is a list (C N)
+; where C is a key and N is a number.
+; returns a vector where entry of ele has increased by count.
+(define (add-ele-count counts ele count)
+  (let [(index (vector-index (lambda (p) (equal? (car p) ele)) counts))]
+    (if index
+      (begin
+	(vector-set! counts index (list ele (+ count (cadr (vector-ref counts index)))))
+	counts)
+      (vector-append counts (vector (list ele count))))))
+
+; count amount of each character in input string.
+; returns vector of lists where car is a character and cadr is the amount of it in input
+; sorted from most common to least common
+(define (count-chars str)
+  (let [(count (vector))]
+    (string-for-each (lambda (c) (set! count (add-ele-count count c 1))) str)
+    count))
+
+; print result to console
+(define (display-subtracted-most-least-elements elements)
+  (let* [(elements (vector-sort (lambda (l r) (> (cadr l) (cadr r))) elements))
+	 (most-common (vector-ref elements 0))
+	 (least-common (vector-ref elements (- (vector-length elements) 1)))]
+    (printf "Most common ~a (~a) - least common ~a (~a) = ~a~%"
+	    (car most-common) (cadr most-common)
+	    (car least-common) (cadr least-common)
+	    (- (cadr most-common) (cadr least-common)))))
+
+; returns a vector counting the number of each consecutive characters in str
+(define (count-pairs str)
+  (let [(len-1 (- (string-length str) 1))]
+    (let loop [(n 0) (pairs '#())]
+      (if (< n len-1)
+	(loop (+ n 1)
+	      (let [(pair (list (string-ref str n) (string-ref str (+ n 1))))]
+		(add-ele-count pairs pair 1)))
+	pairs))))
+
+; count the number of elements where given pairs-count is a vector
+; with amounts of pairs of elements
+; #(((a b) N) ((c d) N') ...)
+(define (count-elements pairs-count)
+  (vector-fold
+    (lambda (index elements-count pair-count)
+      (let [(pair (car pair-count))
+	    (count (cadr pair-count))]
+	(set! elements-count (add-ele-count elements-count (car pair) count))
+	(add-ele-count elements-count (cadr pair) count)))
+    '#() pairs-count))
+
+; directly computes resulting element amounts of
+; inserting elements in input polymer up to depth steps
+; returns vector of lists where car is an element's character and cadr is the amount of it
+(define (polymerize polymer table depth)
+  (let step [(d 0)
+	     (polymer-pairs (count-pairs polymer))
+	     (candidate-pairs '#())]
+    (if (< d depth)
+      (let [(new-polymer-pairs '#()) (new-candidates '#())]
+	(define (multiply index pair-count)
+	  (let* [(pair (car pair-count))
+		 (count (cadr pair-count))
+		 (element (hashtable-ref table pair #f))]
+	    (if element
+	      (let [(new-pair (list (car pair) element))
+		    (new-candidate (list element (cadr pair)))]
+		(set! new-polymer-pairs (add-ele-count new-polymer-pairs new-pair count))
+		(set! new-candidates (add-ele-count new-candidates new-candidate count)))
+	      (add-ele-count pair count))))
+	(vector-for-each multiply polymer-pairs)
+	(vector-for-each multiply candidate-pairs)
+	(step (+ d 1) new-polymer-pairs new-candidates))
+      (let [(elements (count-elements polymer-pairs))
+	    (last (string-ref polymer (- (string-length polymer) 1)))]
+	(add-ele-count elements last 1)))))
+
+(call-with-input-file
+  "input"
+  (lambda (file)
+    (let* [(polymer (get-line file))
+	   (table (begin
+		    (get-line file) ; skip empty line
+		    (read-table file)))]
+      (let loop [(n 0) (polymer polymer)]
+	(if (< n 10)
+	  (loop (+ n 1) (insert polymer table))
+	  (begin
+	    (printf "part 1:~% After 10 polymerization steps: ~% ")
+	    (display-subtracted-most-least-elements (count-chars polymer)))))
+      (printf "part 2:~% After 40 polymerization steps: ~% ")
+      (display-subtracted-most-least-elements (polymerize polymer table 40)))))

14-extended-polymerization/input

@@ -0,0 +1,102 @@
+OHFNNCKCVOBHSSHONBNF
+
+SV -> O
+KP -> H
+FP -> B
+VP -> V
+KN -> S
+KS -> O
+SB -> K
+BS -> K
+OF -> O
+ON -> S
+VS -> F
+CK -> C
+FB -> K
+CH -> K
+HS -> H
+PO -> F
+NP -> N
+FH -> C
+FO -> O
+FF -> C
+CO -> K
+NB -> V
+PP -> S
+BB -> N
+HH -> B
+KK -> H
+OP -> K
+OS -> V
+KV -> F
+VH -> F
+OB -> S
+CN -> H
+SF -> K
+SN -> P
+NF -> H
+HB -> V
+VC -> S
+PS -> P
+NK -> B
+CV -> P
+BC -> S
+NH -> K
+FN -> P
+SH -> F
+FK -> P
+CS -> O
+VV -> H
+OC -> F
+CC -> N
+HK -> N
+FS -> P
+VF -> B
+SS -> V
+PV -> V
+BF -> V
+OV -> C
+HO -> F
+NC -> F
+BN -> F
+HC -> N
+KO -> P
+KH -> F
+BV -> S
+SK -> F
+SC -> F
+VN -> V
+VB -> V
+BH -> O
+CP -> K
+PK -> K
+PB -> K
+FV -> S
+HN -> K
+PH -> B
+VK -> B
+PC -> H
+BO -> H
+SP -> V
+NS -> B
+OH -> N
+KC -> H
+HV -> F
+HF -> B
+HP -> S
+CB -> P
+PN -> S
+BK -> K
+PF -> N
+SO -> P
+CF -> B
+VO -> C
+OO -> K
+FC -> F
+NV -> F
+OK -> K
+NN -> O
+NO -> O
+BP -> O
+KB -> O
+KF -> O

16-packet-decoder/code.scm

@@ -0,0 +1,129 @@
+(import (srfi :43)) ; vector extensions 
+
+(define (>> x n) (bitwise-arithmetic-shift-right x n))
+(define (<< x n) (bitwise-arithmetic-shift-left x n))
+(define (& x n) (bitwise-and x n))
+
+; str is a string of hexadecimal numbers
+; bit-reader returns a closure that iterators over the bits
+; defined by the hex numbers over the requested amount.
+; if 'position is sent to closure instead of a number,
+; the current bit position in the stream is returned.
+(define (bit-reader str)
+  (let [(index -1)
+	(len (string-length str))
+	(available 0)
+	(nibble #f)]
+    (lambda (want)
+      (case want
+	['position (+ (* index 4) (- 4 available))]
+	[else 
+	  (let reader [(want want)]
+	    (when (= available 0)
+	      (set! index (+ index 1))
+	      (set! nibble 
+		(if (< index len)
+		  (string->number (substring str index (+ index 1)) 16)
+		  #f))
+	      (set! available 4))
+	    (if nibble
+	      (let* [(consume (min want available))
+		     (offset (- 4 consume))
+		     (mask (- (<< 1 consume) 1))
+		     (result (>> (& nibble (<< mask offset)) offset))]
+		(set! nibble (<< nibble consume))
+		(set! available (- available consume))
+		(if (< consume want)
+		  (let [(left (- want consume))]
+		    (+ (<< result left) (reader left)))
+		  result))
+	      #f))]))))
+
+; given a bit-reader, this decodes a variable width integer
+; where each packet is 5 bits and a leading bit of 1 tells
+; there is one more packet to read
+(define (decode-integer br)
+  (let loop [(value 0)]
+    (let* [(more? (= (br 1) 1))
+	   (bits (br 4))
+	   (value (+ (* value 16) bits))]
+      (if more?
+	(loop value)
+	value))))
+
+; this decodes each packet in the given hex string
+; calling visitor for each with the version type and value of each packet
+; for a packet of type 4, value is the literal value of the packet
+; for other packets, value is the number of arguments to the opcode.
+(define (decode str visitor)
+  (let [(br (bit-reader str))]
+    (let loop ()
+      (let* [(version (br 3))
+	     (type (br 3))]
+	(if (= type 4)
+	  (visitor version type (decode-integer br))
+	  (let [(length-type (br 1))]
+	    (if (= length-type 0)
+	      (let* [(to-decode (br 15))
+		     (start (br 'position))]
+		(let sub [(count 1)]
+		  (loop)
+		  (if (< (- (br 'position) start) to-decode)
+		    (sub (+ count 1))
+		    (visitor version type count))))
+	      (let [(count (br 11))]
+		(let sub [(n count)]
+		  (loop)
+		  (if (> n 1)
+		    (sub (- n 1))
+		    (visitor version type count)))))))))))
+
+; returns the sum of all version numbers of all the packets in the given encoded BITS stream
+(define (sum-versions str)
+  (let [(sum-version 0)]
+    (decode str (lambda (version type value)
+		  (set! sum-version (+ version sum-version))))
+    sum-version))
+
+; given a stack, pops "value" as many elements
+; and returns a stack with a new head with
+; op concatenated with the popped values.
+; the rest of the original stack follows
+(define (do-op op stack value)
+  (let rec [(stack stack) (got 0) (output '())]
+    (if (= got value)
+      (cons (cons op output) stack)
+      (let [(v (car stack))]
+	(rec (cdr stack) (+ got 1) (cons v output))))))
+
+; we can't use regular scheme operators for the evaluation of the BITS stream
+; because they return #t/#f instead of 1 0
+; so these 3 are helpers to solve the situation
+(define (greater-than a b) (if (> a b) 1 0))
+(define (less-than a b) (if (< a b) 1 0))
+(define (equal-to a b) (if (= a b) 1 0))
+
+; decodes the operation given by the BITS encoded stream and evaluates it
+(define (evaluate str)
+  (let [(stack '())]
+    (decode str
+	    (lambda (version type value)
+	      (set! stack
+		(case type
+		  [0 (do-op '+ stack value)]
+		  [1 (do-op '* stack value)]
+		  [2 (do-op 'min stack value)]
+		  [3 (do-op 'max stack value)]
+		  [4 (cons value stack)]
+		  [5 (do-op 'greater-than stack value)]
+		  [6 (do-op 'less-than stack value)]
+		  [7 (do-op 'equal-to stack value)]))))
+    (eval (car stack))))
+
+(call-with-input-file
+  "input"
+  (lambda (file)
+    (let [(data (get-line file))]
+      (printf "part 1:~% Sum of version numbers ~a~%" (sum-versions data))
+      (printf "part 2:~% Transmission value: ~a~%" (evaluate data)))))
+

16-packet-decoder/input

@@ -0,0 +1 @@
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

18-snailfish/code.scm

@@ -0,0 +1,147 @@
+(import (srfi :13)) ; string extensions
+
+; returns a new string where all occurrences of `find` have been replaced by `replace`
+(define (string-substitute str find replace)
+  (let [(len-find (string-length find))]
+    (let loop [(str str)]
+      (let [(index (string-contains str find))]
+	(if index
+	  (loop (string-replace str replace index (+ index len-find)))
+	  str)))))
+
+; turns a snailfish number into a regular scheme list
+(define (snailfish-number->list str)
+  ; this feels like cheating x)
+  (get-datum
+    (open-string-input-port
+      (string-substitute str "," " "))))
+
+; loads all the snailfish numbers from the given text port, one by line
+(define (load-numbers port)
+  (let loop [(numbers '())]
+    (if (eof-object? (peek-char port))
+      (reverse numbers)
+      (loop (cons (snailfish-number->list (get-line port)) numbers)))))
+
+; updates literal from snailfish number at given index
+(define (update-literal! number index updater)
+  (let [(i 0)]
+    (let rec [(p number)]
+      (if (null? p)
+	i
+	(if (number? (car p))
+	  (if (= i index)
+	    (begin
+	      (set-car! p (updater (car p)))
+	      (set! i #f)) ; kill recursion
+	    (begin
+	      (set! i (+ i 1))
+	      (rec (cdr p))))
+	  (begin
+	    (rec (car p))
+	    (when i
+	      (rec (cdr p)))))))))
+
+; change literal at given index to be given value
+(define (set-literal! number index value)
+  (update-literal! number index (lambda (v) value)))
+
+; increment literal at given index by given value
+(define (add-literal! number index value)
+  (update-literal! number index (lambda (v) (+ v value))))
+
+; change the car of the cdr of l
+(define (set-cadr! l v)
+  (set-car! (cdr l) v))
+
+; explode snailfish number if possible
+; returns #t if any number has exploded 
+(define (explode! input)
+  (let [(index 0)]
+    (let look [(parent '()) (set-parent! #f) (depth 0) (pair input)]
+      (if (not (number? pair))
+	(if (>= depth 4)
+	  ; explode
+	  (let [(left (car pair))
+		(right (cadr pair))]
+	    (add-literal! input (- index 1) left)
+	    (add-literal! input (+ index 2) right)
+	    (set-parent! parent 0)
+	    (set! index #f)) ; kill recursion
+	  (begin
+	    (look pair set-car! (+ depth 1) (car pair))
+	    (when index
+	      (look pair set-cadr! (+ depth 1) (cadr pair)))))
+	; pair is actually a number
+	(set! index (+ index 1))))
+    (not index)))
+
+; split snailfish number if possible
+; returns #t if any number has been split
+(define (split! input)
+  (let [(index 0)]
+    (let look [(pair input)]
+      (if (number? pair)
+	(if (>= pair 10)
+	  (begin
+	    ; split
+	    (set-literal! input index (list (div pair 2) (- pair (div pair 2))))
+	    (set! index #f) ; kill recursion
+	    (reduce! input))
+	  (set! index (+ index 1)))
+	(begin
+	  (look (car pair))
+	  (when index ; check recursion hasn't been killed
+	    (look (cadr pair))))))
+    (not index)))
+
+; reduce snailfish number according to the rules of the problem
+(define (reduce! input)
+  (if (explode! input)
+    (reduce! input)
+    (if (split! input)
+      (reduce! input)
+      input)))
+
+; adds two snailfish numbers
+; input will be corrupted!
+(define (add! a b)
+  (reduce! (list a b)))
+
+; compute magnitude of snailfish number
+(define (magnitude n)
+  (if (number? n)
+    n
+    (+ (* 3 (magnitude (car n)))
+       (* 2 (magnitude (cadr n))))))
+
+; deep copy given list
+(define (duplicate lst)
+  (if (pair? lst)
+    (cons (duplicate (car lst)) (duplicate (cdr lst)))
+    lst))
+
+; finds the largest magnitude obtained by summing any two numbers from the given list
+(define (largest-magnitude numbers)
+  (let [(largest 0)]
+    (for-each
+      (lambda (n1)
+	(for-each
+	  (lambda (n2)
+	    (let* [(sum (add! (duplicate n1) (duplicate n2)))
+		   (mag (magnitude sum))]
+	      (when (> mag largest)
+		(set! largest mag))))
+	  (remove n1 numbers)))
+	numbers)
+    largest))
+
+(call-with-input-file
+  "input"
+  (lambda (file)
+    (let [(numbers (load-numbers file))]
+      (let [(numbers (duplicate numbers))]
+	(printf "part 1:~% Magnitude of final sum: ~a~%"
+		(magnitude (fold-left add! (car numbers) (cdr numbers)))))
+      (printf "part 2:~% Largest magnitude: ~a~%"
+	      (largest-magnitude numbers)))))

18-snailfish/input

@@ -0,0 +1,100 @@
+[[[[9,5],[9,4]],[[6,5],[7,0]]],4]
+[[[5,2],[[7,2],1]],[[[7,5],[0,8]],[[6,9],[7,3]]]]
+[[[9,7],[0,1]],9]
+[1,[[7,3],[[3,7],[3,2]]]]
+[[9,[[0,8],7]],[[3,1],[[6,6],[9,0]]]]
+[4,[[4,4],[[7,7],1]]]
+[[[[6,2],[5,1]],[[3,3],9]],[7,[[5,7],[5,0]]]]
+[[[[4,8],[4,9]],[1,[9,3]]],[1,[1,[6,1]]]]
+[[[[4,7],[3,4]],[8,3]],[[3,7],[0,[1,8]]]]
+[[[6,[4,8]],[4,5]],[4,[1,3]]]
+[[[0,7],0],[[6,[1,8]],[9,[7,9]]]]
+[[[[4,8],[3,9]],[4,5]],[1,1]]
+[[[4,2],[0,[6,7]]],[[[1,8],2],[8,8]]]
+[[[[1,1],7],5],[[6,[5,6]],[6,[7,5]]]]
+[[[[3,2],5],[[5,3],1]],[[[0,4],[9,6]],9]]
+[[6,[7,6]],9]
+[[[[4,0],[0,1]],7],1]
+[[[[1,3],4],6],[[1,[4,2]],[1,4]]]
+[[[[6,9],[4,1]],[[6,3],[0,8]]],[[4,0],[[3,2],[2,9]]]]
+[[[3,6],[[2,0],[3,2]]],[2,5]]
+[[[[4,3],5],5],[[4,[4,0]],6]]
+[[[[4,0],3],[[3,5],8]],[[8,[4,4]],[[9,9],[4,1]]]]
+[[[2,7],6],1]
+[[[[5,3],[8,4]],[0,0]],4]
+[[[0,[8,1]],0],3]
+[[[6,5],[8,2]],[[[6,9],[6,1]],[9,9]]]
+[0,[[4,9],6]]
+[[9,[[9,9],4]],[[[4,7],1],2]]
+[[8,0],[[[0,7],6],[[6,4],2]]]
+[[1,[[2,4],8]],1]
+[[[[1,3],4],[[1,3],0]],[[[1,2],3],2]]
+[[[[2,1],2],[5,[2,8]]],[2,[[6,0],2]]]
+[[[8,[1,0]],[[6,7],[9,6]]],[[2,[9,7]],5]]
+[[[3,[2,0]],[[3,2],[0,0]]],[[[4,6],[9,4]],[[7,8],[5,1]]]]
+[[3,[[9,9],[7,2]]],[[1,3],[2,[3,2]]]]
+[4,[4,[[9,5],6]]]
+[[[[5,7],7],[[3,4],0]],[[9,[8,2]],[2,3]]]
+[[[[2,1],[5,7]],4],[[[6,3],8],[[1,6],[5,1]]]]
+[[[4,4],[[0,9],[7,8]]],[[2,[2,5]],5]]
+[1,[5,[[3,7],[8,2]]]]
+[[[[9,5],[8,6]],[5,5]],[[[9,2],8],[[9,3],[3,8]]]]
+[0,[[9,5],[[3,7],7]]]
+[[[8,[0,4]],[[2,9],6]],[[6,[8,0]],4]]
+[[0,[3,5]],[[5,[0,1]],[[3,6],7]]]
+[[2,[7,1]],[[[5,0],[7,7]],[[2,3],9]]]
+[[5,[9,[3,9]]],[[8,[3,7]],[[7,6],[3,0]]]]
+[[[4,[2,5]],5],[3,1]]
+[[[[4,3],1],[[5,7],6]],[0,[3,1]]]
+[[8,9],[[[0,7],5],[6,[5,7]]]]
+[[6,8],[[5,8],[[8,2],[6,0]]]]
+[[1,[5,6]],5]
+[[[6,1],[9,[1,2]]],1]
+[[5,[7,[4,8]]],[[4,[2,9]],5]]
+[[[2,2],[[7,1],3]],[[[9,7],[4,6]],[1,[0,1]]]]
+[[3,[6,[4,5]]],2]
+[[[0,2],[[8,1],[0,6]]],[[7,[9,6]],0]]
+[[[[1,0],[5,1]],[[0,6],5]],[[[1,8],8],[[0,2],5]]]
+[[6,[[3,6],6]],[[[9,7],[6,4]],[[9,5],1]]]
+[[[0,[5,6]],[9,0]],[[2,9],9]]
+[1,[[4,[9,3]],0]]
+[[1,0],[[1,9],[4,8]]]
+[[[9,3],[7,0]],[[[5,1],[3,8]],9]]
+[[[3,9],[[5,9],2]],[[7,2],1]]
+[[1,[[3,0],[7,6]]],[7,[8,1]]]
+[0,[6,[[7,1],[1,1]]]]
+[[4,[[5,0],[2,1]]],[[[8,8],[8,1]],7]]
+[[[[9,3],[4,3]],4],[7,5]]
+[[9,[[7,4],[8,3]]],[[[1,9],7],[[1,6],[3,1]]]]
+[[6,9],[5,[0,[5,1]]]]
+[[[8,7],3],[[4,8],[0,7]]]
+[[[[3,1],2],[[1,6],[4,3]]],[0,6]]
+[[5,[[5,4],3]],[[8,8],9]]
+[[5,[3,[4,5]]],[[2,[6,0]],[6,1]]]
+[[[[9,5],3],6],[[8,[1,9]],[[5,2],5]]]
+[[[7,5],[[3,6],4]],[6,[[5,1],[0,1]]]]
+[[1,[[4,8],[1,3]]],7]
+[[4,[[4,0],5]],[[[6,2],7],[[4,8],[4,9]]]]
+[[[[2,3],[0,9]],[7,2]],[4,5]]
+[[[[7,7],[8,0]],[7,7]],[[[6,6],[3,2]],[4,[4,3]]]]
+[[[[8,7],6],[[5,5],0]],[[6,[7,3]],[[4,1],[1,7]]]]
+[[[2,[2,2]],[[5,2],1]],[[9,[9,2]],6]]
+[[[[1,7],6],[[8,8],5]],[6,[1,[1,7]]]]
+[[[[8,6],[3,2]],[[5,2],[2,0]]],[[[8,7],2],[[5,5],2]]]
+[[[8,[9,0]],[[9,5],[7,5]]],[[5,1],[[1,1],[4,6]]]]
+[5,[9,[[0,2],7]]]
+[8,[[0,[4,9]],[[7,4],9]]]
+[[[[2,9],5],[[0,6],[6,6]]],[[0,6],[[4,2],[9,9]]]]
+[7,[[[4,3],3],[[5,4],[6,0]]]]
+[[0,[8,[1,1]]],5]
+[[[1,8],[[4,6],[9,7]]],[[[6,6],[2,6]],[4,3]]]
+[[0,[[7,5],[9,9]]],[[9,7],[6,2]]]
+[[[9,[3,0]],[[1,4],0]],[[1,1],1]]
+[[[0,7],[[3,0],8]],[[6,[8,0]],[[4,5],[4,0]]]]
+[[[[2,9],[4,2]],[5,[9,3]]],[4,[2,[3,4]]]]
+[[[1,[7,3]],[[5,7],0]],[6,[[6,5],2]]]
+[4,5]
+[[7,9],[6,[[6,5],[1,0]]]]
+[[4,[[7,5],8]],[[4,0],[[6,6],[0,4]]]]
+[[[9,[7,7]],[[4,2],7]],4]
+[[0,[0,3]],5]

18-snailfish/simple

@@ -0,0 +1,10 @@
+[[[0,[5,8]],[[1,7],[9,6]]],[[4,[1,2]],[[1,4],2]]]
+[[[5,[2,8]],4],[5,[[9,9],0]]]
+[6,[[[6,2],[5,6]],[[7,6],[4,7]]]]
+[[[6,[0,7]],[0,9]],[4,[9,[9,0]]]]
+[[[7,[6,4]],[3,[1,3]]],[[[5,5],1],9]]
+[[6,[[7,3],[3,2]]],[[[3,8],[5,7]],4]]
+[[[[5,4],[7,7]],8],[[8,3],8]]
+[[9,3],[[9,9],[6,[4,9]]]]
+[[2,[[7,7],7]],[[5,8],[[9,3],[0,2]]]]
+[[[[5,2],5],[8,[3,7]]],[[5,[7,5]],[4,4]]]

20-trench-map/code.scm

@@ -0,0 +1,77 @@
+(load "../common.scm")
+
+; returns a vector of the same length of input string
+; where all values are 0 except for when the corresponding
+; entry in the string is '#' which will have a 1 instead.
+(define (string->bin-vector str)
+  (vector-unfold
+    (lambda (i)
+      (if (char=? (string-ref str i) #\#) 1 0))
+    (string-length str)))
+
+; returns a binary matrix loaded from the file
+; all the lines are expected to be the same lengths
+(define (file->matrix file)
+  (let loop [(data '())]
+    (if (eof-object? (peek-char file))
+      (matrix-from-data (reverse-list->vector data))
+      (loop (cons (string->bin-vector (get-line file)) data)))))
+
+; palette enhancing algorihtm: 
+; for each pixel in input image
+; gather all pixels around it to form a 3x3 matrix
+; turn that matrix into a binary number, row by row
+; look up new pixel value in input palette
+(define (enhance image palette steps)
+  (let* [(new-width (+ (matrix-width image) 4))
+	 (new-height (+ (matrix-height image) 4))
+	 (new-image (filled-matrix new-width new-height 0))
+	 (top-left (matrix-get image 0 0 0))
+	 ; if palette 0 is 1, outside becomes all 1 each odd iteration
+	 (outside (if (= (vector-ref palette 0) 1) (mod steps 2) 0))]
+    (update-matrix!
+      new-image
+      (lambda (x y v)
+	(vector-ref palette (+ (* (matrix-get image (- x 3) (- y 3) outside) 256)
+			       (* (matrix-get image (- x 2) (- y 3) outside) 128)
+			       (* (matrix-get image (- x 1) (- y 3) outside) 64)
+			       (* (matrix-get image (- x 3) (- y 2) outside) 32)
+			       (* (matrix-get image (- x 2) (- y 2) outside) 16)
+			       (* (matrix-get image (- x 1) (- y 2) outside) 8)
+			       (* (matrix-get image (- x 3) (- y 1) outside) 4)
+			       (* (matrix-get image (- x 2) (- y 1) outside) 2)
+			       (* (matrix-get image (- x 1) (- y 1) outside) 1)))))
+    (if (<= steps 1)
+      new-image
+      (enhance new-image palette (- steps 1)))))
+
+; for debugging purposes
+; output a PGM 1bpp image file from a given binary matrix
+(define (matrix->image-file matrix filename)
+  (when (file-exists? filename)
+    (delete-file filename))
+  (call-with-output-file
+    filename
+    (lambda (file)
+      (fprintf file "P1~%~a ~a~%" (matrix-width matrix) (matrix-height matrix))
+      (vector-for-each
+	(lambda (y line)
+	  (vector-for-each 
+	    (lambda (x pixel) (fprintf file "~a " (- 1 pixel))) line)
+	  (fprintf file "~%"))
+	(matrix-data matrix)))))
+
+(call-with-input-file
+  "input"
+  (lambda (file)
+    (let* [(enhancer (string->bin-vector (get-line file)))
+	  (image (begin
+		   (get-line file) ; skip empty line
+		   (file->matrix file)))]
+      (let [(enhanced-2 (enhance image enhancer 2))]
+	(printf "part 1:~% Lit pixels after enhancing twice: ~a~%"
+		(matrix-sum enhanced-2))
+	(let [(enhanced-50 (enhance enhanced-2 enhancer 48))]
+	  (printf "part 2:~% Lit pixels after enhancing fifty times: ~a~%"
+		  (matrix-sum enhanced-50)))))))
+

20-trench-map/input

@@ -0,0 +1,102 @@
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21-dirac-dice/code.scm

@@ -0,0 +1,137 @@
+(load "../common.scm")
+
+(define (read-starting-positions filename)
+  (call-with-input-file
+    filename
+    (lambda (file)
+      (let* [(player-1 (begin
+			 (get-string-n file (string-length "Player 1 starting position: "))
+			 (get-number file)))
+	     (player-2 (begin
+			 (get-string-n file (string-length "Player 2 starting position: "))
+			 (get-number file)))]
+	(values player-1 player-2)))))
+
+; returns a lambda that yields increasing numbers from 1 to 100, then repeating back from 1
+(define (deterministic-dice)
+  (let [(value -1)]
+    (lambda ()
+      (set! value (mod (+ value 1) 100))
+      (+ value 1))))
+
+; play a game of dirac with a magic deterministic dice that always yields increasing values
+; returned value is multiplication of dice roll count and final score of opponent
+(define (play-deterministic position-1 position-2 win-score)
+  (let [(dice (deterministic-dice))]
+    ; we subtract one from position so that we can just use "mod 10" to wrap around
+    (let repeat [(player-1 (cons (- position-1 1) 0)) ; each player pair is (position . score)
+		 (player-2 (cons (- position-2 1) 0)) 
+		 (rolls 3)]
+      (let* [(new-position (mod (+ (car player-1) (dice) (dice) (dice)) 10))
+	     ; add 1 to account for off by 1 positions
+	     (new-score (+ new-position (cdr player-1) 1))]
+	(if (>= new-score win-score)
+	  (* (cdr player-2) rolls)
+	  ; swap players in next iteration
+	  (repeat player-2 (cons new-position new-score) (+ 3 rolls)))))))
+
+; state of an universe playing dirac, two players pawn position with their scores
+(define-record-type state
+  (fields
+    ; positions are 0..9 instead of input's 1..10
+    ; so we can just mod 10 while incrementing position
+    (mutable position-1) 
+    (mutable score-1)
+    (mutable position-2) 
+    (mutable score-2)))
+
+(define (state-copy state)
+  (make-state
+    (state-position-1 state)
+    (state-score-1 state)
+    (state-position-2 state)
+    (state-score-2 state)))
+
+(define (state-equal? l r)
+  (and (equal? (state-position-1 l) (state-position-1 r))
+       (equal? (state-position-2 l) (state-position-2 r))
+       (equal? (state-score-1 l) (state-score-1 r))
+       (equal? (state-score-2 l) (state-score-2 r))))
+
+(define (state-hash state)
+  (+ (state-position-1 state)
+     (* 6700417 (+ (state-position-2 state)
+		   (* 6700417 (+ (state-score-1 state)
+				 (* 6700417 (state-score-2 state))))))))
+
+(define (make-state-hashtable)
+  (make-hashtable state-hash state-equal?))
+
+(define (hashtable-for-each proc ht)
+  (let-values [((k v) (hashtable-entries ht))]
+    (vector-for-each (lambda (i k v) (proc k v)) k v)))
+
+(define (hashtable-empty? ht)
+  (= (hashtable-size ht) 0))
+
+; sum and amount of permutations of 3 3-sided dice
+(define dirac-dice
+  '((3 . 1)   ; (1 1 1)
+    (4 . 3)   ; (1 1 2) (1 2 1) (2 1 1)
+    (5 . 6)   ; (1 1 3) (1 2 2) (1 3 1) (2 1 2) (2 2 1) (3 1 1)
+    (6 . 7)   ; (1 2 3) (1 3 2) (2 1 3) (2 2 2) (2 3 1) (3 1 2) (3 2 1)
+    (7 . 6)   ; (1 3 3) (2 2 3) (2 3 2) (3 1 3) (3 2 2) (3 3 1) 
+    (8 . 3)   ; (2 3 3) (3 2 3) (3 3 2)
+    (9 . 1))) ; (3 3 3)
+
+; roll dice creating as many necessary universes in the process
+; returns amount of wins obtained with this call and new states
+(define (dirac-roll win-score states player)
+  (let-values [((get-position get-score set-position! set-score!)
+		(if (= player 1) 
+		  (values state-position-1 state-score-1
+			  state-position-1-set! state-score-1-set!)
+		  (values state-position-2 state-score-2
+			  state-position-2-set! state-score-2-set!)))]
+    (let [(additional-wins 0)
+	  (new-states (make-state-hashtable))]
+      (for-each
+	(lambda (outcome)
+	  (let [(sum (car outcome))
+		(permutations (cdr outcome))]
+	    (hashtable-for-each
+	      (lambda (state amount)
+		(let* [(new-position (mod (+ (get-position state) sum) 10))
+		       (new-score (+ (get-score state) new-position 1))
+		       (universes (* amount permutations))]
+		  (if (>= new-score win-score)
+		    (set! additional-wins (+ additional-wins universes))
+		    (let [(new-state (state-copy state))]
+		      (set-position! new-state new-position)
+		      (set-score! new-state new-score)
+		      (hashtable-set! new-states new-state 
+				      (+ universes (hashtable-ref new-states new-state 0)))))))
+	      states)))
+	dirac-dice)
+      (values additional-wins new-states))))
+
+; play dirac dice starting from given positions up until the given score
+; returned value is maximum number of wins for any of the two players
+(define (play-dirac position-1 position-2 win-score)
+  (let [(init-state (make-state-hashtable))]
+    (hashtable-set! init-state (make-state (- position-1 1) 0 (- position-2 1) 0) 1)
+    ; "states" tracks the amount of universes currently using a given state
+    (let repeat [(states init-state) (player-1-wins 0) (player-2-wins 0) (player 1)]
+      (let-values [((additional-wins new-states)
+		    (dirac-roll win-score states player))]
+	(set! player-1-wins (+ player-1-wins additional-wins))
+	(if (hashtable-empty? new-states) ; have all universes finished playing?
+	  (max player-1-wins player-2-wins)
+	  ; swap players in next iteration
+	  (repeat new-states player-2-wins player-1-wins (- 1 player)))))))
+
+(let-values [((position-1 position-2) (read-starting-positions "input"))]
+  (printf "part 1:~% Rolls * Opponent Score = ~a~%"
+	  (play-deterministic position-1 position-2 1000))
+  (printf "part 2:~% Max Winning Universes: ~a~%"
+	  (play-dirac position-1 position-2 21)))

21-dirac-dice/input

@@ -0,0 +1,2 @@
+Player 1 starting position: 10
+Player 2 starting position: 6

22-reactor-reboot/code.scm

@@ -0,0 +1,74 @@
+(load "../common.scm")
+
+(define (read-cuboid-operation file)
+  (let* [(on/off (if (symbol=? (get-datum file) 'on) 1 0))
+	 (x-start (begin (get-string-n file 3) (get-number file))) ; skipping " x="
+	 (x-end (begin (get-string-n file 1) (get-number file)))   ; skipping dot
+	 (y-start (begin (get-string-n file 2) (get-number file))) ; skipping "y="
+	 (y-end (begin (get-string-n file 1) (get-number file)))   ; skipping dot
+	 (z-start (begin (get-string-n file 2) (get-number file))) ; skipping "z="
+	 (z-end (begin (get-string-n file 1) (get-number file)))]  ; skipping dot
+    (list on/off x-start x-end y-start y-end z-start z-end)))
+
+(define (load-cuboid-ops filename)
+  (call-with-input-file
+    filename
+    (lambda (file)
+      (let loop [(ops '())]
+	(if (eof-object? (peek-char file))
+	  (reverse ops)
+	  (loop (cons (read-cuboid-operation file) ops)))))))
+
+(define (make-3d-vector x-size y-size z-size init)
+  (let x-loop [(x 0) (planes '())]
+    (if (= x x-size)
+      (reverse-list->vector planes)
+      (x-loop (+ x 1)
+	      (cons
+		(let y-loop [(y 0) (lines '())]
+		  (if (= y y-size)
+		    (reverse-list->vector lines)
+		    (y-loop (+ y 1) (cons (make-vector z-size init) lines))))
+		planes)))))
+
+; set 3D volume to given value
+; end ranges are inclusive!
+(define (vector-3d-set! 3d-vector value x-start x-end y-start y-end z-start z-end)
+  (let [(width (- (vector-length (vector-ref (vector-ref 3d-vector 0) 0)) 1))
+	(height (- (vector-length (vector-ref 3d-vector 0)) 1))
+	(depth (- (vector-length 3d-vector) 1))]
+    (let x-loop [(x (max x-start 0))]
+      (unless (> x (min x-end width))
+	(let y-loop [(y (max y-start 0))]
+	(unless (> y (min y-end height))
+	  (let z-loop [(z (max z-start 0))]
+	  (unless (> z (min z-end depth))
+	    (vector-set! (vector-ref (vector-ref 3d-vector x) y) z value)
+	    (z-loop (+ z 1))))
+	(y-loop (+ y 1))))
+    (x-loop (+ x 1))))))
+
+(define (vector-3d-sum 3d-vector)
+  (vector-fold
+    (lambda (i a v)
+      (+ a (vector-fold
+	     (lambda (i a v)
+	       (+ a (vector-fold
+		      (lambda (i a v) (+ a v))
+		      0 v)))
+	     0 v)))
+    0 3d-vector))
+
+(let [(operations (load-cuboid-ops "input"))
+      (grid (make-3d-vector 101 101 101 0))]
+  (let operate [(op operations)]
+    (unless (null? op)
+      (apply vector-3d-set! grid
+	     (cons (caar op) 
+		   ; offset x/y/z ranges from -50..50 to 0..101 to fit in 3d-vector
+		   (map (lambda (x) (+ x 50)) (cdar op))))
+      (operate (cdr op))))
+  (printf "part 1:~% Cubes powered after initialization procedure: ~a~%"
+	  (vector-3d-sum grid)))
+
+;; do step 2 using a sparse voxel octree ?

22-reactor-reboot/input

@@ -0,0 +1,420 @@
+on x=-40..11,y=-14..32,z=-31..22
+on x=-12..41,y=-30..15,z=-32..21
+on x=-9..44,y=-33..17,z=-4..45
+on x=-18..35,y=-40..10,z=-38..9
+on x=-24..30,y=-11..39,z=-13..37
+on x=-41..9,y=-36..10,z=-23..26
+on x=-43..9,y=-29..18,z=-19..29
+on x=-10..38,y=-36..12,z=-38..11
+on x=-49..-3,y=-34..10,z=-7..37
+on x=-48..2,y=-2..45,z=-6..41
+off x=21..38,y=10..24,z=-28..-12
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+off x=-13..0,y=-39..-23,z=-14..-4
+on x=-49..-4,y=-35..18,z=-42..4
+off x=-40..-25,y=-4..7,z=-28..-9
+on x=-6..40,y=-26..24,z=-31..15
+off x=-14..-1,y=-4..15,z=-28..-16
+on x=-14..37,y=-11..41,z=-44..5
+off x=10..23,y=7..16,z=0..12
+on x=-18..29,y=-21..26,z=-13..39
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+on x=13527..35092,y=-39535..-24365,z=56377..70036
+off x=-70137..-37611,y=-24509..-8532,z=57202..67742
+on x=39807..55755,y=10601..32443,z=-68086..-50437
+off x=-37020..-11107,y=-79773..-50762,z=27827..48699
+off x=20430..35135,y=2362..25602,z=-84324..-59379
+on x=-74640..-65651,y=4902..18156,z=32787..51162
+on x=-44225..-26007,y=67721..89795,z=-17083..-2827
+off x=-23754..3967,y=62633..86609,z=13865..33457
+off x=-60583..-41519,y=-1047..12455,z=52556..73365
+off x=-50992..-32598,y=16389..45404,z=-62485..-41273
+off x=15311..44826,y=61278..74010,z=-55050..-34344
+off x=14490..32695,y=70832..90434,z=5184..16444
+on x=30484..62070,y=56490..73608,z=-43714..-22849
+on x=46871..61357,y=-69427..-48446,z=-4288..13867
+on x=-76779..-46596,y=-49541..-37133,z=3286..27263
+off x=13477..50993,y=-81349..-64857,z=4744..11305
+on x=63474..90005,y=12735..32459,z=-38155..-20233
+on x=-75674..-40443,y=28889..48697,z=26683..38419
+on x=-46985..-36144,y=53432..74680,z=-22168..3725
+off x=-69357..-49593,y=-4107..21625,z=-73460..-56882
+on x=-42033..-9137,y=61001..79202,z=4274..34898
+on x=-7911..27236,y=48363..63805,z=-56831..-44785

24-arithmetic-logic-unit/code.scm

@@ -0,0 +1,62 @@
+(define (load-instructions filename)
+  (call-with-input-file
+    filename
+    (lambda (file)
+      (let loop [(instructions '())]
+	(let [(instruction (get-datum file))]
+	  (cond
+	    [(eof-object? instruction)
+	     (reverse instructions)]
+	    [(symbol=? instruction 'inp)
+	     (loop (cons (list instruction
+			       (get-datum file)) instructions))]
+	    [else 
+	      (loop (cons (list instruction
+				(get-datum file)
+				(get-datum file)) instructions))]))))))
+
+(define (digits-from-number n)
+  (let loop [(n n) (digits '())]
+    (if (= n 0)
+      digits
+      (loop (div n 10) (cons (mod n 10) digits)))))
+
+(define (interpret-with-input instructions input)
+  (let [(enviro '((x 0) (y 0) (z 0) (w 0)
+			(inp (lambda (n)
+			       (let [(digit (car input))]
+				 (set! input (cdr input))
+				 digit)))
+			(add +)
+			(mul *)
+			(eql (lambda (a b) (if (= a b) 1 0)))))
+	(input (digits-from-number input))]
+    (eval (list 'let*
+		; base environment with input
+		(cons (list 'input (cons 'list input)) enviro)
+		; code adapted to be able to modify environment
+		(cons 'begin (map 
+		  (lambda (i)
+		    (list 'set! (cadr i) i))
+		  instructions))
+		; return value
+		'(list x y z w)))))
+
+(define (trace instructions input)
+  (let loop [(already '())
+	     (instructions instructions)]
+    (unless (null? instructions)
+      (printf "~20a: ~a~%"
+	      (car instructions)
+	      (interpret-with-input (cons (car instructions)
+					  (reverse already))
+				    input))
+      (loop (cons (car instructions) already)
+	    (cdr instructions)))))
+
+(define (biggest-valid-MONAD instructions)
+  0) ; no idea what x, y, z and w mean...
+
+(let [(instructions (load-instructions "input"))]
+  (printf "part 1: ~% Biggest valid MONAD: ~a~%"
+	  (biggest-valid-MONAD instructions)))

24-arithmetic-logic-unit/input

@@ -0,0 +1,252 @@
+inp w
+mul x 0
+add x z
+mod x 26
+div z 1
+add x 12
+eql x w
+eql x 0
+mul y 0
+add y 25
+mul y x
+add y 1
+mul z y
+mul y 0
+add y w
+add y 15
+mul y x
+add z y
+inp w
+mul x 0
+add x z
+mod x 26
+div z 1
+add x 14
+eql x w
+eql x 0
+mul y 0
+add y 25
+mul y x
+add y 1
+mul z y
+mul y 0
+add y w
+add y 12
+mul y x
+add z y
+inp w
+mul x 0
+add x z
+mod x 26
+div z 1
+add x 11
+eql x w
+eql x 0
+mul y 0
+add y 25
+mul y x
+add y 1
+mul z y
+mul y 0
+add y w
+add y 15
+mul y x
+add z y
+inp w
+mul x 0
+add x z
+mod x 26
+div z 26
+add x -9
+eql x w
+eql x 0
+mul y 0
+add y 25
+mul y x
+add y 1
+mul z y
+mul y 0
+add y w
+add y 12
+mul y x
+add z y
+inp w
+mul x 0
+add x z
+mod x 26
+div z 26
+add x -7
+eql x w
+eql x 0
+mul y 0
+add y 25
+mul y x
+add y 1
+mul z y
+mul y 0
+add y w
+add y 15
+mul y x
+add z y
+inp w
+mul x 0
+add x z
+mod x 26
+div z 1
+add x 11
+eql x w
+eql x 0
+mul y 0
+add y 25
+mul y x
+add y 1
+mul z y
+mul y 0
+add y w
+add y 2
+mul y x
+add z y
+inp w
+mul x 0
+add x z
+mod x 26
+div z 26
+add x -1
+eql x w
+eql x 0
+mul y 0
+add y 25
+mul y x
+add y 1
+mul z y
+mul y 0
+add y w
+add y 11
+mul y x
+add z y
+inp w
+mul x 0
+add x z
+mod x 26
+div z 26
+add x -16
+eql x w
+eql x 0
+mul y 0
+add y 25
+mul y x
+add y 1
+mul z y
+mul y 0
+add y w
+add y 15
+mul y x
+add z y
+inp w
+mul x 0
+add x z
+mod x 26
+div z 1
+add x 11
+eql x w
+eql x 0
+mul y 0
+add y 25
+mul y x
+add y 1
+mul z y
+mul y 0
+add y w
+add y 10
+mul y x
+add z y
+inp w
+mul x 0
+add x z
+mod x 26
+div z 26
+add x -15
+eql x w
+eql x 0
+mul y 0
+add y 25
+mul y x
+add y 1
+mul z y
+mul y 0
+add y w
+add y 2
+mul y x
+add z y
+inp w
+mul x 0
+add x z
+mod x 26
+div z 1
+add x 10
+eql x w
+eql x 0
+mul y 0
+add y 25
+mul y x
+add y 1
+mul z y
+mul y 0
+add y w
+add y 0
+mul y x
+add z y
+inp w
+mul x 0
+add x z
+mod x 26
+div z 1
+add x 12
+eql x w
+eql x 0
+mul y 0
+add y 25
+mul y x
+add y 1
+mul z y
+mul y 0
+add y w
+add y 0
+mul y x
+add z y
+inp w
+mul x 0
+add x z
+mod x 26
+div z 26
+add x -4
+eql x w
+eql x 0
+mul y 0
+add y 25
+mul y x
+add y 1
+mul z y
+mul y 0
+add y w
+add y 15
+mul y x
+add z y
+inp w
+mul x 0
+add x z
+mod x 26
+div z 26
+add x 0
+eql x w
+eql x 0
+mul y 0
+add y 25
+mul y x
+add y 1
+mul z y
+mul y 0
+add y w
+add y 15
+mul y x
+add z y

common.scm

@@ -1,3 +1,27 @@
+(import (srfi :43)) ; vector extensions
+
+; get list of lines from a file
+(define (get-lines file)
+  (let loop [(lines '())]
+    (if (eof-object? (peek-char file))
+      lines
+      (loop (cons (get-line file) lines)))))
+
+; reads a numnber from input
+; also consumes the next non-number character in the file!
+(define (get-number file)
+  (let [(sign 1)]
+    (let loop [(index 0) (n 0)]
+      (let [(c (get-char file))]
+	(cond
+	  [(char-numeric? c)
+	   (loop (+ index 1) (+ (char->number c) (* n 10)))]
+	  [(and (char=? c #\-)
+		(= index 0))
+	   (set! sign -1)
+	   (loop 1 n)]
+	  [else (* sign n)])))))
+
 ; returns a list of numbers parsed from the first line of the file,
 ; separated by commas
 (define (read-comma-separated-numbers file)
@@ -6,9 +30,99 @@
       (cond
 	[(char=? c #\,) (loop (cons n draws) 0)]
 	[(char-whitespace? c) (reverse (cons n draws))]
-	[else (loop draws (+ (* n 10) (string->number (string c))))]))))
+	[else (loop draws (+ (* n 10) (char->number c)))]))))
 
 ; returns numbers 0 to 9 from ascii character
 (define (char->number c)
   (- (char->integer c) 48)) ; 48 is ASCII's number zero
 
+(define-record-type matrix (fields width height data))
+
+; builds a matrix record from the given 2D vector
+; vectors inside data vector are expected to all be the same length
+(define (matrix-from-data data)
+  (make-matrix
+    (vector-length (vector-ref data 0))
+    (vector-length data)
+    data))
+
+; returns a matrix object of given dimensions full of zeroes
+(define (filled-matrix width height filler)
+  (matrix-from-data
+    (do [(i 0 (+ i 1))
+	 (v '() (cons (make-vector width filler) v))]
+      ((>= i height) (list->vector v)) '())))
+
+; returns value at x,y coordinates in matrix
+; if coordinate is out of bounds, returns default
+(define (matrix-get matrix x y default)
+  (if (or (< x 0)
+	  (< y 0)
+	  (>= x (matrix-width matrix))
+	  (>= y (matrix-height matrix)))
+    default
+    (vector-ref (vector-ref (matrix-data matrix) y) x)))
+
+; set value at x,y in matrix with given one
+; if coordinate is out of bounds, nothing happens
+(define (matrix-set! matrix x y value)
+  (when (and (>= x 0)
+	     (>= y 0)
+	     (< x (matrix-width matrix))
+	     (< y (matrix-height matrix)))
+    (vector-set! (vector-ref (matrix-data matrix) y) x value)))
+
+; print matrix line by line to console
+; each line will be displayed as a scheme-vector
+(define (matrix-print matrix)
+  (let y-loop [(y 0)]
+    (printf "~a~%" (vector-ref (matrix-data matrix) y))
+    (when (< y (- (matrix-height matrix) 1))
+      (y-loop (+ y 1)))))
+
+; parse 0-9 numerical data from file and return a matrix
+(define (load-matrix file)
+  (let y-loop [(heightmap '())]
+    (let x-loop [(line '())]
+      (let [(c (get-char file))]
+	(cond
+	  [(eof-object? c)
+	   (matrix-from-data (reverse-list->vector heightmap))]
+	  [(char-whitespace? c)
+	   (y-loop (cons (reverse-list->vector line) heightmap))]
+	  [(char-numeric? c)
+	   (x-loop (cons (char->number c) line))])))))
+
+; matrix visitor
+; calls function with all coordinates of matrix and value at corresponding point
+; value returned by function is set at the visiting coordinate
+(define (update-matrix! matrix function)
+  (let [(data (matrix-data matrix))
+	(width-1 (- (matrix-width matrix) 1))
+	(height-1 (- (matrix-height matrix) 1))]
+    (let y-loop [(y 0)]
+      (let x-loop [(x 0)]
+	(let [(value (vector-ref (vector-ref data y) x))]
+	  (vector-set! (vector-ref data y) x
+		       (function x y value))
+	  (when (< x width-1)
+	    (x-loop (+ x 1)))))
+      (when (< y height-1)
+	(y-loop (+ y 1))))))
+
+; increase by 1 value at x,y in given matrix
+; return that value too
+(define (matrix-inc! matrix x y)
+  (let [(v (+ 1 (matrix-get matrix x y 0)))]
+    (matrix-set! matrix x y v)
+    v))
+
+; sum all values of matrix
+(define (matrix-sum matrix)
+  (vector-fold
+    (lambda (y sum line)
+      (+ sum
+	 (vector-fold
+	   (lambda (x sum value) (+ sum value))
+	   0 line)))
+    0 (matrix-data matrix)))