665. Non-decreasing Array

665. Non-decreasing Array (Easy)

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

Related Topics:
Array

Solution 1.

// OJ: https://leetcode.com/problems/non-decreasing-array/
// Author: github.com/lzl124631x
// Time: O(N)
// Space: O(1)
class Solution {
public:
    bool checkPossibility(vector<int>& A) {
        for (int i = 1, cnt = 0; i < A.size(); ++i) {
            if (A[i] >= A[i - 1]) continue;
            if (++cnt > 1) return false;
            if (i - 2 < 0 || min(A[i], A[i - 1]) >= A[i - 2]) A[i] = A[i - 1] = min(A[i], A[i - 1]);
            else A[i] = A[i - 1] = max(A[i], A[i - 1]);
        }
        return true;
    }
};