Two solution to the Coin Change Kata in Clojure

gistfile1.clj

(ns coins.core)

;;; Solution I
;;; recursive, with coin hash as a parameter
(defn make-coins-rec [coins amount h] ;; all possible solutions in a nested list
  "return all valid solutions"
  (cond
   (zero? amount) h
   (pos? amount) (map #(make-coins-rec coins (- amount %) (update-in h [%] inc)) coins)))

(defn make-coins [coins amount]
  "take the best solution"
    (->>
     (make-coins-rec coins amount (zipmap coins (repeat 0)))
     flatten
     (filter (comp not nil?))
     (sort-by #(reduce + (vals %)))
     first
     (filter (comp pos? val))
     (into {})
     ))

;; test
(make-coins [1 5 10 25] 18)

;;; Solution II
;;; recursive, with coin hash as a return value
(defn make-coins-rec2 [coins amount]
  "return all valid solutions"
  (cond
   (zero? amount) (list {})
   (pos? amount) (for [c coins
                       sol (make-coins-rec2 coins (- amount c))
                       :let [update-sol (update-in sol [c] (fnil inc 0))]]
                   update-sol)
  ))
     

(defn make-coins2 [coins amount]
  "take the best solution"
  (apply min-key #(reduce + (vals %))
         (make-coins-rec2 coins amount)))


;; test
(make-coins2 [1 5 10 25] 18)