solve day 13 part 1

1 files changed, 40 insertions, 0 deletions

diff --git a/13/1.rkt b/13/1.rkt
new file mode 100644
index 0000000..21c29c3
--- /dev/null
+++ b/13/1.rkt
@@ -0,0 +1,40 @@
+#lang racket
+
+(require "../lib/utils.rkt")
+
+(define lines
+  (call-with-input-file "input"
+    (λ (fp) (get-lines fp))))
+
+(define patterns (split-list-by "" lines))
+
+(define (find-reflection lines)
+  (define lines-vec (list->vector lines))
+  (define len (vector-length lines-vec))
+  (define (find-first)
+    (let loop ((i 0) (ret '()))
+      (if (>= i (- len 1))
+          (reverse ret)
+          (if (string=? (vector-ref lines-vec i)
+                        (vector-ref lines-vec (+ i 1)))
+              (loop (+ 1 i) (cons i ret))
+              (loop (+ 1 i) ret)))))
+  (define (count start)
+    (let loop ((cnt 1) (i start))
+      (if (or (< i 0)
+              (>= (+ start cnt) len))
+          (+ start 1)
+          (if (string=? (vector-ref lines-vec i)
+                        (vector-ref lines-vec (+ start cnt)))
+              (loop (+ 1 cnt) (- i 1))
+              0))))
+  (define start (find-first))
+  (if (null? start)
+      0
+      (apply max (map count start))))
+
+(define (score pattern)
+  (+ (* 100 (find-reflection pattern))
+     (find-reflection (transpose-list pattern))))
+
+(apply + (map score patterns))