The Change Maker Kata - http://rubyquiz.com/quiz154.html

change_maker.clj

(ns change-maker.core-test
  (:require [clojure.test :refer :all]))

(def ^:dynamic *denominations* [25 10 5 1])

(defn best-match [value]
  (first (filter #(<= % value) *denominations*)))

(defn calculate-change [value product]
  (let [reducer (best-match value)]
    (if (= 0 value)
      product
      (recur (- value reducer)
             (conj product reducer)))))

(defn denoms []
  (loop [coll *denominations*
         result []]
    (if (empty? coll)
      result
      (recur (rest coll) (conj result coll)))))

(defn permutations [value]
  (map #(binding [*denominations* %]
          (calculate-change value []))
       (denoms)))

(defn least-number-of-coins [variations]
  (first (sort-by count variations)))

(defn make-change [value]
  (let [results (permutations value)]
    (least-number-of-coins results)))

(deftest change-maker
  (are [x y] (= x (make-change y))
    [25] 25
    [25 10 10] 45
    [25 10 1 1 1 1] 39)
  (binding [*denominations* [10 7 1]]
    (are [x y] (= x (make-change y))
      [10 7] 17
      [7 7] 14)))

(deftest denoms-test
  (binding [*denominations* [3 2 1]]
    (is (= [[3 2 1] [2 1] [1]] (denoms)))))