665-non-decreasing-array

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Description

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

Solution(Python)

class Solution:
    def checkPossibility(self, N: List[int]) -> bool:
        err = 0
        for i in range(1, len(N)):
            if N[i] < N[i-1]:
                if err or (i > 1 and i < len(N) - 1 and N[i-2] > N[i] and N[i+1] < N[i-1]):
                    return False
                err = 1
        return True