clojure实现最长上升子序队列算法

4Clojure上的一道题：4Clojure 最长上升子序列算法
描述如下：


Given a vector of integers, find the longest consecutive sub-sequence of increasing numbers. If two sub-sequences have the same length, use the one that occurs first. An increasing sub-sequence must have a length of 2 or greater to qualify.


例：
[1 0 1 2 3 0 4 5]的最长上升子序列为 [0 1 2 3]
[5 6 1 3 2 7]的最长上升子序列为 [5 6]

(defn test [coll]
;使用map存放每个起始元素的上升队列，key无意义，仅用于标记不同的队列
(loop [flag 0
     tmp-result {flag [(first coll)]}
     index 0]
  (if (< index (- (count coll) 1))
    (let [current (nth coll index)
          next (nth coll (inc index))]
    (if (> next current)
      ;如果下一个元素大于当前元素，把下一个元素加入到当前元素的队列中，flag就是key，保持不变
     (recur flag (assoc tmp-result flag (conj (tmp-result flag) next)) (inc index))
      ;否则说明新的队列开始了，新建一个队列，key为flag+1，value为下一个元素
     (recur (inc flag) (assoc tmp-result (inc flag) [next]) (inc index))))
  ;得到结果之后筛选最长的队列
  (let [tmp (vals tmp-result)]
    (loop [final (first tmp)
           s (next tmp)]
      (if (first s)
        (if (>= (count (first s)) (count final))
          (recur (first s) (next s))
          (recur final (next s)))
        ;队列长度至少为2
        (if (> (count final) 1)
          final
          [])))))))

另外一种实现：

(defn test [coll]
  (let [pairs (partition 2 1 coll)
        ; 分组：first与last大小比较
        group-pairs (partition-by #(< (first %) (last %)) pairs)
        ; 保留first大于last的pair
        filter-pairs (filter #(every? (fn [pair] (< (first pair) (last pair))) %) group-pairs)
        ; 
        rise-seq (map #(concat 
                          (first %) 
                          ; 取pair的最后一个数字
                          (map last (rest %))) 
                      filter-pairs)
        candidate (reverse rise-seq)]
        (if 
          (empty? candidate)
          []
          (apply (partial max-key count) candidate))))

最终结果：

<!-- lang: vb -->
user=> (test [5 6 1 3 2 7])
[5 6]
user=> (test [1 0 -1 3 0])
[-1 3]
user=> (test [1 0 1 2 3 0 4 5])
[0 1 2 3]