LeetCode | 665. Non-decreasing Array

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).

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

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

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

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