[leetcode] 665. Non-decreasing Array

Given an array with n integers, your task is to check if it could become non-decreasing by modifying at most 1 element.

We define an array is non-decreasing if array[i] <= array[i + 1] holds for every i (1 <= i < n).

Example 1:

Input: [4,2,3]
Output: True
Explanation: You could modify the first 4 to 1 to get a non-decreasing array.

Example 2:

Input: [4,2,1]
Output: False
Explanation: You can't get a non-decreasing array by modify at most one element.

Note: The n belongs to [1, 10000].

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不满足条件的array必然满足以下条件之一：

存在至少两个[a,b]对（其中a > b）；

存在类似于[3,4,2,3]的子序列；

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我的代码如下：

class Solution {
public:
    bool checkPossibility(vector<int>& nums) {
        if (nums.size() <= 2) return true;
        if (nums[0] <= nums[1]) {
            int error = 0;
            for (int i = 1; i < nums.size() - 1; i++) {
                if (nums[i] > nums[i+1]) {
                    error++;
                    if (i <= nums.size() - 3 && nums[i-1] > nums[i+1] && nums[i] > nums[i+2]) return false;
                    if (error > 1) return false;
                }
            }
            return true;
        } else {
            for (int i = 1; i < nums.size() - 1; i++) {
                if (nums[i] > nums[i+1]) return false;
            }
            return true;
        }
    }
};