clojure解数学问题

最近群里有个问题

把987654321这9个数从大到小顺序排列,添上十丶一号,使结果等于90

刚好在学习clojure就试着用clojure写代码来搜索答案了

clojure的表现力还是很强的，总共写了20来行代码

(ns my-stuff.core
  (:gen-class))

(defn convert-tree [tree]
  (if (number? tree)
    tree
    (let [[a b c] tree]
      (if (= a +)
        (list (convert-tree b) "+" (convert-tree c))
        (list (convert-tree b) "-" (convert-tree c))))))

(defn recursion [t c]
  (let [l (last t)
        p (drop-last 1 t)]
    (if (== c 1)
      (if (not= 1 (count t))
        (if (== 90 (eval t))
          (println (flatten (convert-tree t)))))
      (let [nc (dec c)
            n (+ (* 10 l) nc)
            nt (if (== 1 (count t)) (first t) t )]
        (recursion (reverse (conj (reverse p) n))  nc)
        (recursion (list + nt nc)  nc)
        (recursion (list - nt nc)  nc)))))

(defn -main
  "I don't do a whole lot ... yet."
  [& args]
  (recursion (list 9),9))

输出

(98 + 7 + 6 - 54 + 32 + 1)

(98 + 7 - 6 + 5 + 4 + 3 - 21)

(98 + 7 - 6 - 5 - 4 + 3 - 2 - 1)

(98 + 7 - 6 - 5 - 4 - 3 + 2 + 1)

(98 - 7 + 6 - 5 + 4 - 3 - 2 - 1)

(98 - 7 + 6 - 5 - 4 + 3 - 2 + 1)

(98 - 7 - 65 + 43 + 21)

(98 - 7 - 6 + 5 + 4 - 3 - 2 + 1)

(98 - 7 - 6 + 5 - 4 + 3 + 2 - 1)

(98 - 7 - 6 - 5 + 4 + 3 + 2 + 1)

(9 + 8 + 76 + 5 - 4 - 3 - 2 + 1)

(9 + 8 + 76 - 5 + 4 - 3 + 2 - 1)

(9 + 8 + 76 - 5 - 4 + 3 + 2 + 1)

(9 + 8 + 7 + 6 + 54 + 3 + 2 + 1)

(9 + 8 + 7 - 6 + 54 - 3 + 21)

(9 - 8 + 76 + 5 + 4 + 3 + 2 - 1)

clojure交流群里的大神说可以利用clojure.core.logic来解决，继续研究ing