581. Shortest Unsorted Continuous Subarray

Given an integer array, you need to find one continuous subarray that if you only sort this subarray in ascending order, then the whole array will be sorted in ascending order, too.

You need to find the shortest such subarray and output its length.

Example 1:

Input: [2, 6, 4, 8, 10, 9, 15]Output: 5Explanation: You need to sort [6, 4, 8, 10, 9] in ascending order to make the whole array sorted in ascending order.

Note:

1. Then length of the input array is in range [1, 10,000].
2. The input array may contain duplicates, so ascending order here means <=.

找到不符合递增顺序的子序列。

一开始没想到好的办法去解决，将排序好的数组与原数组一一比对，没想到还是过了。。。

在讨论中看到的一种办法非常巧妙。数组中第i个数应该是前i个数中最大的最大值，若不是，则不满足要求。

public class Solution {    public int findUnsortedSubarray(int[] A) {            int n = A.length, beg = -1, end = -2, min = A[n-1], max = A[0];            for (int i=1;i<n;i++) {                max = Math.max(max, A[i]); //当前的最大值                min = Math.min(min, A[n-1-i]);                if (A[i] < max) end = i;                if (A[n-1-i] > min) beg = n-1-i;            }            return end - beg + 1;        }}