day 4

src/day4.clj

@@ -0,0 +1,88 @@
+(ns day4
+  (:require [clojure.string :as string]
+            [helpers :refer [get-input]]))
+
+(def input-example
+"MMMSXXMASM
+MSAMXMSMSA
+AMXSXMAAMM
+MSAMASMSMX
+XMASAMXAMM
+XXAMMXXAMA
+SMSMSASXSS
+SAXAMASAAA
+MAMMMXMMMM
+MXMXAXMASX")
+
+;(def input (string/split-lines input-example))
+(def input (string/split-lines (get-input 4)))
+(def line-len (count input))
+(def column-len (count (first input)))
+
+(defn get-string [coords]
+  (->>
+   coords
+   (map #(get-in input %))
+   (apply str)))
+
+(defn diag [[x0 y0]]
+  (loop [x x0 y y0 d []]
+    (if (or (< x 0) (< y 0) (> x column-len ) (> y line-len))
+      d (recur (dec x) (inc y) (conj d [x y])))))
+
+(defn flip [d]
+  (mapv (fn [[x y]] [(dec (- line-len x)) y]) d))
+
+(def diagonals
+  (let [diagonals
+        (->>
+         (concat
+          (map #(vector % 0) (range line-len))
+          (map #(vector (dec line-len) %) (range 1 column-len)))
+         (map diag))]
+    (->>
+     (concat diagonals (map flip diagonals))
+     (map get-string))))
+
+(defn check-line [l]
+  (re-seq #"XMAS" l))
+
+(def result
+  (let [lines input
+        columns (->> (map seq lines)
+                     (apply interleave)
+                     (partition column-len)
+                     (map (partial apply str)))
+        rev-fn (fn [i] (map #(apply str (reverse %)) i))]
+    (->>
+     (concat
+      lines (rev-fn lines)
+      columns (rev-fn columns)
+      diagonals (rev-fn diagonals))
+     (map check-line)
+     (apply concat))))
+
+(println "XMAS appears" (count result) "times.")
+
+(defn x-mas? [[x y]]
+  (let [w1 (get-string [[(dec x) (dec y)] [x y] [(inc x) (inc y)]])
+        w2 (get-string [[(dec x) (inc y)] [x y] [(inc x) (dec y)]])]
+    (and (or (= w1 "MAS") (= w1 "SAM"))
+         (or (= w2 "MAS") (= w2 "SAM")))))
+
+(def result2
+  (let [m (mapv vec input)]
+    (->>
+     (map-indexed
+      (fn [x l]
+        (map-indexed
+         (fn [y c]
+           (when (= \A c) [x y]))
+         l))
+      m)
+     (apply concat)
+     (remove nil?)
+     (map x-mas?)
+     (filter true?))))
+
+(println "X-MAS appears" (count result2) "times")