From d0842f0de1c0a3370ba3fe49918f664863bac100 Mon Sep 17 00:00:00 2001
From: lamp
Date: Mon, 11 Dec 2023 13:34:24 +0000
Subject: add day 8 solutions

---
 8-2.scm | 40 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)
 create mode 100755 8-2.scm

(limited to '8-2.scm')

diff --git a/8-2.scm b/8-2.scm
new file mode 100755
index 0000000..7e68044
--- /dev/null
+++ b/8-2.scm
@@ -0,0 +1,40 @@
+#!/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)))
+
+(define (solve-path start tree instructions)
+  (let ((current-instruction 0)
+        (current-node start)
+        (count 0))
+    (while (not (equal? (string-ref current-node 2) #\Z))
+      (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)))
+    count))
+
+(let* ((port (open-input-file "8.txt"))
+       (lines (read-lines port))
+       (instructions (car lines))
+       (tree (map parse-line (cddr lines)))
+       (start-nodes (filter (lambda (x) (equal? (string-ref x 2) #\A)) (map car tree))))
+  (close-port port)
+  (display (apply lcm (map (lambda (x) (solve-path x tree instructions)) start-nodes))))
-- 
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