day 11 part 2

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))

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
+    (visit-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
+    (visit-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

common.scm

@@ -1,3 +1,5 @@
+(import (srfi :43)) ; vector extensions
+
 ; returns a list of numbers parsed from the first line of the file,
 ; separated by commas
 (define (read-comma-separated-numbers file)
@@ -12,3 +14,86 @@
 (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 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 (visit-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)))