665. Non-decreasing Array

Problem Link

Description

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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 cannot get a non-decreasing array by modifying at most one element.

 

Constraints:

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

Solution

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Python3

class Solution:
    def checkPossibility(self, nums):
 
        if len(nums) < 3: return True
        
        count = 0
        for i in range(1, len(nums)):
            if nums[i-1] > nums[i]:
                count += 1
                if count > 1:
                    return False
                if i < 2 or nums[i-2] <= nums[i]:
                    nums[i-1] = nums[i]
                else:
                    nums[i] = nums[i-1]
                
        return count <= 1