Advent of Code 2015 - day 1.

core.clj

(ns day-1.core)

(def input (slurp "input.txt"))

(def up \()

(defn where-is-santa
  "What floor will Santa finish on after following INSTRUCTIONS?"
  [instructions]
  (reduce #(+ %1
              (if (= %2 up)
                1
                -1))
          0
          instructions))

(defn first-basement-floor
  "The index of the first instruction in INSTRUCTIONS that mean that Santa goes
   into a basement floor."
  [instructions]
  (loop [floor 0
         i     instructions
         c     0]
    (if (= floor -1)
      c
      (recur (+ floor
                (if (= (first i) up)
                  1
                  -1))
             (rest i)
             (inc c)))))