greedy change

coin_core.clj

(ns coin.core)

(def no-change {1 0 5 0 10 0 25 0})

(def coins [25 10 5 1])

(defn count-change
  [change]
  (reduce
   (fn [value coin]
      (let [n-coins (get change coin)]
        (+ (* n-coins coin) value)))
    0
    (keys change)))

(defn make-change
  [amount]
  (first
    (reduce
      (fn [[chg amt] coin]
        (let [n-coins (quot amt coin)
              remaining-amt (rem amt coin)]
          [(assoc chg coin n-coins) remaining-amt]))
      [no-change amount]
      coins)))