leetcode 581

class Solution {
public:
    int findUnsortedSubarray(vector<int>& nums) {
        vector<int> t = nums;
        sort(t.begin(), t.end());
        int start = 0, end = nums.size() -1;
        while (start < nums.size() && t[start] == nums[start]) ++start;
        // cout << start << endl;
        while (end > start &&t[end] == nums[end]) --end;
        // cout << end << endl;
        return end - start + 1;
    }
};

class Solution {
public:
    // max递增序列最大值，从头开始
    // min递减序列最小值，从尾开始
    // end 从前向后扩展，start从后向前扩展
    // 理解为寻找逆序对的end和start位置
    // 当前数若是小于递增序列的最大值，则存在逆序对
    int findUnsortedSubarray(vector<int>& nums) {
        int n = nums.size();
        int start = 0, end = -1;
        int max = nums[0], min = nums[n - 1];
        for (int i = 0; i < n; ++i) {
            if (max > nums[i]) {
                end = i;
            } else {
                max = nums[i];
            }
            if (min < nums[n - i - 1]) {
                start = n - i - 1;
            } else {
                min = nums[n - i -1];
            }
            // cout << i <<" : " << end <<" " << start << endl;
        }
        // cout << end << " " << start << endl;
        return end - start + 1;
    }
};