From e51d7a2093cce44c25659b22756f6f05f7044333 Mon Sep 17 00:00:00 2001
From: Oscar Najera <hi@oscarnajera.com>
Date: Sat, 16 Dec 2023 09:38:24 +0100
Subject: part2

---
 AoC2023/day13/solver.lisp | 85 ++++++++++++++++++++++++++---------------------
 1 file changed, 47 insertions(+), 38 deletions(-)

diff --git a/AoC2023/day13/solver.lisp b/AoC2023/day13/solver.lisp
index f149f2e..53cc753 100644
--- a/AoC2023/day13/solver.lisp
+++ b/AoC2023/day13/solver.lisp
@@ -1,4 +1,7 @@
-(ql:quickload '(fiveam))
+;; 6:34
+;; 8:11 part 1
+;; 9:36 part 2
+(ql:quickload '(fiveam arrows cl-ppcre))
 
 (defparameter eg-vert "#...##..#
 #....#..#
@@ -16,26 +19,24 @@
 ..##..##.
 #.#.##.#.")
 
-(defun find-repeat (rows)
-  (loop for (one two-or-nil) on rows by #'cdr
-        for idx from 0
-        when (and (not (null two-or-nil))
-                  (equal one two-or-nil))
-          collect (1+ idx)))
+(defun count-differences (a b)
+  (loop for x across a
+        for y across (or b "")
+        count (not (eq x y))))
 
-(defun find-v-mirror (rows)
-  (remove-if-not (lambda (n) (v-mirror-p rows n))
-                 (find-repeat rows)))
+(defun v-mirror (rows &optional (max-differences 0))
+  (loop
+    for idx from 1 below (length rows)
+    when
+    (= max-differences
+       (loop
+         for above in (reverse (subseq rows 0 idx))
+         for below in (subseq rows idx)
+         sum (count-differences above below)))
+    do (return idx)))
 
-(defun v-mirror-p (rows idx)
-  (every #'equal
-         (reverse (subseq rows 0 idx))
-         (subseq rows idx)))
-
-
-(defun find-h-mirror (rows)
-  (find-v-mirror
-   (transpose-rows rows)))
+(defun h-mirror (rows &optional (max-differences 0))
+  (v-mirror (transpose-rows rows) max-differences))
 
 (defun transpose-rows (rows)
   (arrows:-<>
@@ -46,30 +47,36 @@
 
 (fiveam:test partials
   (fiveam:is
-   (equal '(4)
-          (find-repeat
-           (cl-ppcre:split "\\n" eg-vert))))(fiveam:is
-   (equal '(4)
-          (find-v-mirror
-           (cl-ppcre:split "\\n" eg-vert))))
-
+   (= 4
+      (v-mirror
+       (cl-ppcre:split "\\n" eg-vert))))
   (fiveam:is
-   (equal '(3)
-          (find-repeat
-           (cl-ppcre:split "\\n" eg-horizontal))))
+   (= 1
+      (v-mirror
+       (cl-ppcre:split "\\n" eg-vert) 1)))
   (fiveam:is
-   (null (find-v-mirror
+   (null (v-mirror
           (cl-ppcre:split "\\n" eg-horizontal))))
   (fiveam:is
-   (equal '(5)
-          (find-h-mirror
-           (cl-ppcre:split "\\n" eg-horizontal)))))
+   (= 3 (v-mirror
+         (cl-ppcre:split "\\n" eg-horizontal) 1)))
+  (fiveam:is
+   (= 5
+      (h-mirror
+       (cl-ppcre:split "\\n" eg-horizontal))))
+  (fiveam:is
+   (null (h-mirror
+          (cl-ppcre:split "\\n" eg-horizontal) 1))))
 
-(defun solver (maps)
-  (let ((verical-mirrors (delete nil (mapcan #'find-v-mirror maps)))
-        (horizontal-mirrors (delete nil (mapcan #'find-h-mirror maps))))
+(defun solver (maps &optional (max-differences 0))
+  (let ((vertical-mirrors (delete nil (mapcar (lambda (m)
+                                                (v-mirror m max-differences))
+                                              maps)))
+        (horizontal-mirrors (delete nil (mapcar (lambda (m)
+                                                  (h-mirror m max-differences))
+                                                maps))))
     (+
-     (* 100 (apply #'+ verical-mirrors))
+     (* 100 (apply #'+ vertical-mirrors))
      (apply #'+ horizontal-mirrors))))
 
 (defun parse-input (file)
@@ -80,6 +87,8 @@
 
 (fiveam:test solutions
   (fiveam:is (= 405 (solver (parse-input "eg-in"))))
-  (fiveam:is (= 35360 (solver (parse-input "input")))))
+  (fiveam:is (= 400 (solver (parse-input "eg-in") 1)))
+  (fiveam:is (= 35360 (solver (parse-input "input"))))
+  (fiveam:is (= 36755 (solver (parse-input "input") 1))))
 
 (fiveam:run!)
-- 
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