Initial commit

2021/day05/day05.scm

@@ -0,0 +1,55 @@
+(import (chicken io)
+	srfi-1
+	srfi-42
+	srfi-69
+	srfi-152
+	matchable)
+
+(define (read-input #!optional (port (current-input-port)))
+  (define (parse-entry s)
+    (map (lambda (x) (map string->number (string-split x ",")))
+	 (string-split s " -> ")))
+  (map parse-entry (read-lines port)))
+
+(define (horizontal? line)
+  (match-let ((((x1 y1) (x2 y2)) line))
+    (= x1 x2)))
+
+(define (vertical? line)
+  (match-let ((((x1 y1) (x2 y2)) line))
+    (= y1 y2)))
+
+(define (diagonal? line)
+  (and (not (horizontal? line))
+       (not (vertical? line))))
+
+(define (range x1 x2)
+  (iota (+ 1 (abs (- x2 x1)))
+	x1
+	(if (>= x2 x1) 1 -1)))
+
+(define (all-points lines #!optional (diagonals #f))
+  (define h (make-hash-table #:initial 0))
+  (do-ec (: line lines)
+	 (or (horizontal? line) (vertical? line))
+	 (match-let ((((x1 y1) (x2 y2)) line))
+	   (list-ec (: x (range x1 x2))
+		    (: y (range y1 y2))
+		    (hash-table-update! h (list x y) add1))))
+  (when diagonals
+    (do-ec (: line lines)
+	   (if (diagonal? line))
+	   (match-let ((((x1 y1) (x2 y2)) line))
+	     (list-ec (:parallel (: x (range x1 x2))
+				 (: y (range y1 y2)))
+		      (hash-table-update! h (list x y) add1)))))
+  h)
+
+(define (part12 lines diagonals)
+  (length
+   (filter (lambda (n) (> n 1))
+	   (hash-table-values (all-points lines diagonals)))))
+
+(let ((lines (read-input)))
+  (print (part12 lines #f))
+  (print (part12 lines #t)))