day 2

src/day2.clj

@@ -0,0 +1,52 @@
+(ns day2
+  (:require [clojure.edn :as edn]
+            [clojure.string :as string]
+            [helpers :refer [get-input]]))
+
+
+(def test-input "11-22,95-115,998-1012,1188511880-1188511890,222220-222224,
+1698522-1698528,446443-446449,38593856-38593862,565653-565659,
+824824821-824824827,2121212118-2121212124")
+
+(defn- gen-range [spec]
+  (let [[a b] (string/split (string/trim spec) #"-")
+        a (edn/read-string a)
+        b (inc (edn/read-string b))]
+    (map str (range a b))))
+
+(defn- invalid? [id]
+  (let [c (count id)]
+    (and (even? c)
+         (let [first-half (apply str (take (/ c 2) id))]
+           (string/ends-with? id first-half)))))
+
+;(def input (string/split test-input #","))
+(def input (string/split (get-input 2) #","))
+
+(println
+ "Sum of all invalid IDs:"
+ (->>
+  input
+  (mapcat gen-range)
+  (filter invalid?)
+  (map edn/read-string)
+  (reduce +)))
+
+(defn- invalid?' [id]
+  (if (= 1 (count id))
+    false
+    (let [h (inc (/ (count id) 2))
+          make-ptn (fn [n]
+                     (re-pattern
+                      (str "(" (apply str (take n id)) ")+")))
+          patterns (map make-ptn (range 1 h))]
+      (some #(re-matches % id) patterns))))
+
+(println
+ "Sum of all invalid IDs (part 2):"
+ (->>
+  input
+  (mapcat gen-range)
+  (filter invalid?')
+  (map edn/read-string)
+  (reduce +)))