2 files changed, 97 insertions(+), 0 deletions(-)

A advent09.scm
A day09-example.in

@@ 0,0 1,89 @@
+#!/usr/bin/guile -s
+!#
+
+(use-modules ((ice-9 match) #:select (match))
+             ((srfi srfi-1) #:select (first fold last lset-adjoin))
+             ((srfi srfi-9 gnu) #:select (define-immutable-record-type))
+             ((srfi srfi-64) #:select (test-begin
+                                       test-end
+                                       test-equal))
+             ((f) #:select (read-lines))
+             ((algorithms) #:select (flatten product)))
+
+(define-immutable-record-type <bridge>
+  (bridge counter head tail)
+  bridge?
+  (counter bridge-counter set-bridge-counter)
+  (head bridge-head set-bridge-head)
+  (tail bridge-tail set-bridge-tail))
+
+(define (move-head bridge-record direction)
+  (let* ([head (bridge-head bridge-record)]
+         [x (car head)]
+         [y (cdr head)])
+    (match direction
+     ["U" (set-bridge-head bridge-record (cons x (+ y 1)))]
+     ["D" (set-bridge-head bridge-record (cons x (- y 1)))]
+     ["R" (set-bridge-head bridge-record (cons (+ x 1) y))]
+     ["L" (set-bridge-head bridge-record (cons (- x 1) y))])))
+
+(define (move-tail moved-head)
+  (let* ([head (bridge-head moved-head)]
+         [tail (bridge-tail moved-head)]
+         [head-x (car head)]
+         [head-y (cdr head)]
+         [tail-x (car tail)]
+         [tail-y (cdr tail)])
+    (cond [(= 2 (- head-x tail-x)) (set-bridge-tail moved-head (cons (+ tail-x 1) head-y))]
+          [(= -2 (- head-x tail-x)) (set-bridge-tail moved-head (cons (- tail-x 1) head-y))]
+          [(= 2 (- head-y tail-y)) (set-bridge-tail moved-head (cons head-x (+ tail-y 1)))]
+          [(= -2 (- head-y tail-y)) (set-bridge-tail moved-head (cons head-x (- tail-y 1)))]
+          [else moved-head])))
+
+(define (move bridge-record direction)
+  (let ([moved-head (move-head bridge-record direction)])
+    (move-tail moved-head)))
+
+(define (process-command order bridge-record)
+  (let process-step ([bridge-record bridge-record]
+                     [direction (car order)]
+                     [steps (cdr order)])
+    (if (zero? steps)
+        bridge-record
+        (let ([moved (move bridge-record direction)])
+          (process-step (set-bridge-counter moved
+                               (lset-adjoin equal?
+                                            (bridge-counter moved)
+                                            (bridge-tail moved)))
+                        direction
+                        (- steps 1))))))
+
+(define (part-1 filename)
+  (length (bridge-counter (fold process-command (bridge '((0 . 0)) '(0 . 0) '(0 . 0)) (input filename)))))
+
+(define (part-2 filename)
+  (input filename))
+
+(define (input filename)
+  (map
+   (λ (line)
+     (let ([splitted (string-split line #\space)])
+       (cons (first splitted)
+             (string->number (last splitted)))))
+   (read-lines filename)))
+
+
+;; Part 1
+(display (part-1 "day09.in"))
+(newline)
+;; Part 2
+;; (display (part-2 "day09.in"))
+;; (newline)
+
+;; Tests
+(test-begin "example")
+
+(test-equal "Test part 1" 13 (part-1 "day09-example.in"))
+;; (test-equal "Test part 2" 8 (part-2 "day09-example.in"))
+
+(test-end "example")

@@ 0,0 1,8 @@
+R 4
+U 4
+L 3
+D 1
+R 4
+D 1
+L 5
+R 2<
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