do day 8

2023/src/day08.clj

@@ -0,0 +1,51 @@
+(ns day08
+  (:require [core :refer [get-puzzle-input]]))
+
+(defn parse-map [lines]
+  (->> lines
+       (map #(re-find #"(.*) = \((.*), (.*)\)" %))
+       (map rest)
+       (map (fn [[a b c]] [a [b c]]))
+       (into {})))
+
+(defn get-lcm [x]
+     (let
+       [gcd (fn gcd [a b] (if (= 0 b) a (gcd b (mod a b))))
+        lcm (fn lcm [a b] (/ (* a b) (gcd a b)))]
+     (reduce lcm x)))
+
+(let [[dir _ & lines] (get-puzzle-input 8)
+      dir-idx (map #(condp = %
+                      \L 0
+                      \R 1)
+                   dir)
+      data (parse-map lines)]
+  (loop [node "AAA"
+         [dir-idx & drest] (cycle dir-idx)
+         n 0]
+    (if (= node "ZZZ")
+      n
+      (recur (get (data node) dir-idx)
+             drest
+             (inc n)))))
+
+(let [[dir _ & lines] (get-puzzle-input 8)
+      dir-idx (map #(condp = %
+                      \L 0
+                      \R 1)
+                   dir)
+      data (parse-map lines)
+      starts (->> data
+                  keys
+                  (filter #(= (last %) \A)))]
+  (->> starts
+       (map #(loop [node %
+               [dir-idx & drest] (cycle dir-idx)
+               n 0]
+          (if (= (last node) \Z)
+            n
+            (recur (get (data node) dir-idx)
+                   drest
+                   (inc n)))))
+       (get-lcm)))
+