[AoC2023] day21 part 1 lisp

1 files changed, 43 insertions, 0 deletions

diff --git a/AoC2023/day21/solver.lisp b/AoC2023/day21/solver.lisp
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+++ b/AoC2023/day21/solver.lisp
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+(ql:quickload '(fiveam))
+(defpackage :day21
+  (:use :cl :fiveam))
+(in-package :day21)
+;;22:55
+;;23:32
+
+(defun find-start (field)
+  (destructuring-bind (rows cols)
+      (array-dimensions field)
+    (loop for row below rows do
+      (loop for col below cols do
+        (when (eq (aref field row col) #\S)
+          (return-from find-start (list row col)))))))
+
+(defun next-moves (field)
+  (destructuring-bind (rows cols)
+      (array-dimensions field)
+    (lambda (pos)
+      (destructuring-bind (row col) pos
+        (loop for (dr dc) in '((0 1) (0 -1) (1 0) (-1 0))
+              for nr = (+ row dr)
+              for nc = (+ col dc)
+              when (and (< -1 nr rows)
+                        (< -1 nc cols)
+                        (not (eq #\# (aref field nr nc))))
+                collect (list nr nc))))))
+
+(let* ((lines
+         (uiop:read-file-lines "input"))
+       (field (make-array (list (length lines) (length (car lines)))
+                          :initial-contents lines))
+       (walker (next-moves field)))
+  (labels ((all-places (positions)
+             (delete-duplicates (mapcan walker positions) :test #'equal)))
+
+    (loop
+      repeat 64
+      for positions = (all-places (list (find-start field)))
+        then (all-places positions)
+      ;; do (print positions)
+      finally (return (length positions))))
+  )