[LintCode] Longest Increasing Continuous Subsequence 最长连续递增子序列

Give an integer array，find the longest increasing continuous subsequence in this array.

An increasing continuous subsequence:

• Can be from right to left or from left to right.
• Indices of the integers in the subsequence should be continuous.

 Notice

O(n) time and O(1) extra space.

Have you met this question in a real interview? 

Yes

Example

For [5, 4, 2, 1, 3], the LICS is [5, 4, 2, 1], return 4.

For [5, 1, 2, 3, 4], the LICS is [1, 2, 3, 4], return 4.

这道题跟LeetCode上那道Longest Increasing Subsequence很像，但是比那道题简单，因为这道题需要递增子序列连续，这样我们只要挨个比较一下即可，由于题目中说了左右两个方向递增都行，可以用左右两个方向分别遍历一遍，也可以把两个遍历合并到一起，只用一个循环，同时寻找递增和递减的数列，使用两个变量cnt1和cnt2分别记录最长递增和递减数列的长度，一旦递增递减断开，记得将对应的计数器重置即可，参见代码如下：

class Solution {
public:
    /**
     * @param A an array of Integer
     * @return  an integer
     */
    int longestIncreasingContinuousSubsequence(vector<int>& A) {
        if (A.empty()) return 0;
        int res = 1, cnt1 = 1, cnt2 = 1;
        for (int i = 0; i < A.size() - 1; ++i) {
            if (A[i] < A[i + 1]) {
                ++cnt1; 
                cnt2 = 1;
            } else {
                ++cnt2;
                cnt1 = 1;
            }
            res = max(res, max(cnt1, cnt2));
        }
        return res;
    }
};

类似题目：

Longest Increasing Subsequence