581. Shortest Unsorted Continuous Subarray

Problem:

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: 5
Explanation: 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 <=.

思路：

Solution (C++):

int findUnsortedSubarray(vector<int>& nums) {
    if (nums.empty())  return 0;
    int n = nums.size();
    int no_min_index = -1, no_max_index = n;
    int right_min = nums[n-1], left_max = nums[0];
    
    for (int i = n-2; i >= 0; --i) {
        if (nums[i] <= right_min)  right_min = nums[i];
        else  no_min_index = i;
    }
    if (no_min_index == -1)  return 0;
    for (int i = 1; i < n; ++i) {
        if (nums[i] >= left_max)  left_max = nums[i];
        else  no_max_index = i;
    }
    return no_max_index - no_min_index + 1;
}

性能：

Runtime: 52 ms  Memory Usage: 26.5 MB

思路：

Solution (C++):

性能：

Runtime: ms  Memory Usage: MB