day 10

09-smoke-basin/code.scm

@@ -105,7 +105,7 @@
     low-points))
 
 ; write a PGM file for given heightmap and low points
-; max altitude (9) is white
+; basin limits are grey
 ; basins are red-ish (brighter the higher the point)
 ; low points are bright green
 ;
@@ -148,20 +148,18 @@
 	  (when (< y (- height 1))
 	    (y-loop (+ y 1))))
 
-	; show basins as redish areas
-	; show low points as full green pixels
 	(for-each
 	  (lambda (lp)
-	    ; red channel to max on pixels of basins
+	    ; show basins as redish areas
 	    (visit-basin heightmap lp
 			 (lambda (x y)
 			   (let [(ofs (offset x y))]
 			     (vector-set! data ofs 255))))
-	    ; green channel to max on pixels of low point
+	    ; show low points as bright green
 	    (let [(ofs (offset (low-point-x lp) (low-point-y lp)))]
-	      (vector-set! data ofs 255)
+	      (vector-set! data ofs 0)
 	      (vector-set! data (+ 1 ofs) 255)
-	      (vector-set! data (+ 2 ofs) 255)))
+	      (vector-set! data (+ 2 ofs) 0)))
 	  low-points)
 
 	; write pixels to file

10-syntax-scoring/code.scm

@@ -0,0 +1,107 @@
+; 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)))))
+
+; check if character can close chunk
+(define (closing? c)
+  (case c
+    (#\) #t)
+    (#\} #t)
+    (#\] #t)
+    (#\> #t)
+    (else #f)))
+
+; check if character can close chunk starting by o 
+(define (is-closed-by? o c)
+  (or (and (char=? o #\<) (char=? c #\>))
+      (and (char=? o #\{) (char=? c #\}))
+      (and (char=? o #\() (char=? c #\)))
+      (and (char=? o #\[) (char=? c #\]))))
+
+; return character needed to close chunk started by o
+(define (close o)
+  (case o
+    (#\( #\))
+    (#\{ #\})
+    (#\[ #\])
+    (#\< #\>)
+    (else #f)))
+
+; if given line is corrupt, returns expected character
+(define (corrupt-char? line)
+  (let loop [(i 0)]
+    (if (< i (string-length line))
+      (let [(c (string-ref line i))]
+	(if (closing? c)
+	  i
+	  (let [(close-index (loop (+ i 1)))]
+	    (if (number? close-index)
+	      (let [(d (string-ref line close-index))]
+		(if (is-closed-by? c d)
+		  (loop (+ close-index 1))
+		  d))
+	      close-index))))
+      #t)))
+
+; compute score after syntax checking all given lines
+(define (score-illegal-lines lines)
+  (fold-left
+    (lambda (score line)
+      (+ score
+	 (case (corrupt-char? line)
+	   (#\) 3)
+	   (#\] 57)
+	   (#\} 1197)
+	   (#\> 25137)
+	   (else 0))))
+    0 lines))
+
+; returns #t if line is corrupt
+(define (corrupt? line)
+  (char? (corrupt-char? line)))
+
+(define (not-corrupt? line)
+  (not (corrupt? line)))
+
+; returns list of characters needed to autocomplete the given line
+(define (complete incomplete-line)
+  (let [(stack '())]
+    (string-for-each
+      (lambda (c)
+	(if (closing? c)
+	  (set! stack (cdr stack))
+	  (set! stack (cons c stack))))
+      incomplete-line)
+    (map close stack)))
+
+; returns auto complete score applied to incomplete lines of input
+(define (score-autocomplete lines)
+  (define (score completion)
+    (fold-left
+      (lambda (s c)
+	(+ (* s 5) 
+	   (case c
+	     (#\) 1)
+	     (#\] 2)
+	     (#\} 3)
+	     (#\> 4))))
+      0 completion))
+  (let [(scores (sort <
+		      (map score
+			   (map complete
+				(filter not-corrupt? lines)))))]
+    (list-ref scores (div (length scores) 2))))
+
+(call-with-input-file
+  "input"
+  (lambda (file)
+    (let [(lines (get-lines file))]
+      (printf "part 1:~% Illegal lines score = ~a~%"
+	      (score-illegal-lines lines))
+      (printf "part 2:~% Completed lines score = ~a~%"
+	      (score-autocomplete lines)))))
+
+

10-syntax-scoring/input

@@ -0,0 +1,94 @@
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