Advent of Code 2015 - day 2.

core.clj

(ns day-2.core)

(defn box-dimensions
  "Given the dimensions of a box in the form \"XxYxZ\", return a sorted
   sequence of X, Y and Z."
  [box]
  (sort (map parse-long
             (re-seq #"[0-9]+" box))))

(def boxes
  (map box-dimensions
       (re-seq #"[0-9x]+"
               (slurp "input.txt"))))

(defn paper-for-box
  "The amount of paper required to wrap a box of dimensions X, Y and Z."
  [[x y z]]
  (+ (* 3 x y)
     (* 2 x z)
     (* 2 y z)))

(defn ribbon-for-box
  "The amount of ribbon required to tie a box of dimensions X, Y and Z."
  [[x y z]]
  (+ (* 2 x)
     (* 2 y)
     (* x y z)))

(def paper-for-all-boxes
  (reduce + 
          (map paper-for-box boxes)))

(def ribbon-for-all-boxes
  (reduce + 
          (map ribbon-for-box boxes)))