665. Non-decreasing Array ------------ Median !!!!!~~~~~~~

Q:

Given an array nums 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 nums[i] <= nums[i + 1] holds for every i (0-based) such that (0 <= i <= n - 2).

 

Example 1:

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

Example 2:

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

 

Constraints:

• 1 <= n <= 10 ^ 4
• - 10 ^ 5 <= nums[i] <= 10 ^ 5

A:

要记得修改nums的值。

class Solution {
public:
    bool checkPossibility(vector<int>& nums) {
        nums.insert(nums.begin(),INT_MIN);
        nums.push_back(INT_MAX);
        
        int c = 0;
        for(int i =1;i<nums.size()-1; ++i){ 
            if(nums[i] > nums[i+1] ){ // change at either i or i+1
                c++;
                if(c>=2)
                    return false;
                // now update nums[i] or nums[i-1]  // every time, nums[i] >= nums[i-1]
                if(nums[i-1] > nums[i+1]) // now way to update at i
                    nums[i+1] = nums[i];   // update at i+1
                else
                    nums[i] = nums[i+1];
            }
        }
        return true;
    }
};

要区分更改那种情况