loops - 将值添加到匹配谓词的第一个列表(列表)

Question

我有一个列表列表和一个值。我的目标是一个新的列表列表，其中值被组合(新的第一项)到匹配谓词的第一个列表(例如 > 到列表的第一项)。如果没有列表与谓词匹配，我希望我的值在列表末尾“开始”一个新列表。

if my list is: ['(2 3 4) '(4 5 6 7) '(5 6 7)]
and my value: 3
and my predicate: (comp (partial < my-value) first)
then my result should be: ['(2 3 4) '(3 4 5 6 7) '(5 6 7)]

if my value was: 10
my result should be: ['(2 3 4) '(4 5 6 7) '(5 6 7) '(10)]

这个问题让我感到困惑，因为我的命令式思维一直告诉我它应该多么容易，但我找不到一个简单的(好吧，老实说:任何)解决方案。到目前为止，这是我的尝试:

(defn add-to-first-list-that-matches [func value]
  (loop [result []
         remaining-lists list-of-lists
         value-to-add value]
    (if (empty? remaining-lists)
      result
      (let [current-list (first remaining-lists)
            value-matches? (func value-to-add current-list)
            new-list (if value-matches? (conj value-to-add current-list) current-list)]
        (recur (conj new-list result)
               (rest remaining-lists)
               (if-not value-matches? value-to-add nil))))))

(它崩溃了)请用一些 clojure 表达式魔法启发我 :)

顺便说一句。我想将其作为最长递增子序列问题的一部分来解决。

Answer 1

这使用循环递归。

(defn add-to-ll
  [ll pred value]
  (loop [[current & unprocessed] ll
         processed []]
    (cond
     (pred current) (concat processed
                            [(cons value current)]
                            unprocessed)
     (empty? unprocessed) (concat processed
                                  [current]
                                  [[value]])
     :else (recur unprocessed
                  (conj processed current)))))


 (def l-l1 [[2 3 4] [4 5 6 7] [5 6 7]])
 (add-to-ll l-l1 (comp (partial < 10) first) 10)
 => ([2 3 4] [4 5 6 7] [5 6 7] [10])

 (add-to-ll l-l1 (comp (partial < 3) first) 3)
 => ([2 3 4] (3 4 5 6 7) [5 6 7])

你也可以使用split-with

(defn add-to-ll
  [ll pred value]
  (let [[first-lists [to-change & rest-lists]] (split-with (complement pred) ll)]
    (if to-change
      (concat first-lists [(cons value to-change)] rest-lists)
      (concat ll [[value]]))))

在性能方面，第一个解决方案应该运行得更快一些。