add day 8 solutions

1 files changed, 36 insertions, 0 deletions

diff --git a/8.scm b/8.scm
new file mode 100755
index 0000000..f4025e8
--- /dev/null
+++ b/8.scm
@@ -0,0 +1,36 @@
+#!/usr/bin/env -S guile -s
+!#
+(use-modules (ice-9 regex)
+             (ice-9 textual-ports)
+             (srfi srfi-1)
+             (srfi srfi-69))
+
+(define (read-lines port)
+  (letrec ((loop (lambda (l ls)
+                   (if (eof-object? l)
+                       ls
+                       (loop (get-line port) (cons l ls))))))
+    (reverse (loop (get-line port) '()))))
+
+(define (parse-line line)
+  (let ((m (string-match "([A-Z]{3}) = \\(([A-Z]{3}), ([A-Z]{3})\\)" line)))
+    `(,(match:substring m 1) (,(match:substring m 2) ,(match:substring m 3)))))
+
+(define (find-node tag tree)
+  (car (filter (lambda (x) (equal? tag (car x))) tree)))
+
+(let* ((port (open-input-file "8.txt"))
+       (lines (read-lines port))
+       (instructions (car lines))
+       (tree (map parse-line (cddr lines)))
+       (current-instruction 0)
+       (current-node "AAA")
+       (count 0))
+  (close-port port)
+  (while (not (equal? current-node "ZZZ"))
+    (if (equal? (string-ref instructions current-instruction) #\L)
+        (set! current-node (caadr (find-node current-node tree)))
+        (set! current-node (cadadr (find-node current-node tree))))
+    (set! current-instruction (modulo (1+ current-instruction) (string-length instructions)))
+    (set! count (1+ count)))
+  (display count))