Solve day 13, part 1

Author: archaeologistdev

day-13.clj

@@ -0,0 +1,24 @@
+(ns day-13 (:require [hashp.core]))
+
+(def parse-int #(Long/parseLong %))
+(def input (slurp "input13.txt"))
+(comment (def input "939
+7,13,x,x,59,x,31,19"))
+
+(defn departure-times [bus]
+  {:id bus :times (reductions + 0 (repeat bus))})
+
+(defn departing-after [dep bus]
+  (assoc bus :earliest (first (drop-while #(< % dep) (:times bus)))))
+
+(defn puzzle1 [in]
+  (let [[dep buses](clojure.string/split-lines in)
+        dep (parse-int dep)
+        buses (map parse-int (remove #{"x"} (clojure.string/split buses #",")))]
+    (->> buses
+         (map departure-times)
+         (map #(departing-after dep %))
+         (apply min-key :earliest)
+         (#(* (:id %) (- (:earliest %) dep))))))
+
+(puzzle1 input)

input13.txt

@@ -0,0 +1,2 @@
+1000186
+17,x,x,x,x,x,x,x,x,x,x,37,x,x,x,x,x,907,x,x,x,x,x,x,x,x,x,x,x,19,x,x,x,x,x,x,x,x,x,x,23,x,x,x,x,x,29,x,653,x,x,x,x,x,x,x,x,x,41,x,x,13