Leetcode 665. Non-decreasing Array

[medium]

Given an array nums with n integers, your task is to check if it could become non-decreasing by modifying at most one 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:

• n == nums.length
• 1 <= n <= 104
• -105 <= nums[i] <= 105

[Think]

1. find what kind of situation we will have
2. num[i] < num[i-1] → will need to change nums[i]
3. There are two scenario, first change num[i] to num[i-1]; or num[i-1] to num[i]
4. best way is change to small one, but have to check if i-2 smaller or equal to i, then need to changeit to large num[i]

[Note]

1. Trick part is once number[i] ≥ nums[i-2]