Longest Continuous Increasing Subsequence

Description

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.

Example

Example 1:

Input: [5, 4, 2, 1, 3]
Output: 4
Explanation:
For [5, 4, 2, 1, 3], the LICS  is [5, 4, 2, 1], return 4.

Example 2:

Input: [5, 1, 2, 3, 4]
Output: 4
Explanation:
For [5, 1, 2, 3, 4], the LICS  is [1, 2, 3, 4], return 4.
思路：本题为直接去找一个数组的最长连续上升/下降子序列，直接从左往右枚举即可，每次到单调性变化的时候更新答案。

public class Solution {
    public int longestIncreasingContinuousSubsequence(int[] A) {
        if (A == null || A.length == 0) {
            return 0;
        }

        int n = A.length;
        int answer = 1;

        // from left to right
        int length = 1; // just A[0] itself
        for (int i = 1; i < n; i++) {
            if (A[i] > A[i - 1]) {
                length++;
            } else {
                length = 1;
            }
            answer = Math.max(answer, length);
        }

        // from right to left
        length = 1;
        for (int i = n - 2; i >= 0; i--) {
            if (A[i] > A[i + 1]) {
                length++;
            } else {
                length = 1;
            }
            answer = Math.max(answer, length);
        }

        return answer;
    }
}

　　

Challenge

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