Question:

Given an array 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 array[i] <= array[i + 1] holds for every i (1 <= i < n).

Example:

  1. Input: [4,2,3]
  2. Output: True
  3. Explanation: You could modify the first 4 to 1 to get a non-decreasing array.
  1. Input: [4,2,1]
  2. Output: False
  3. Explanation: You can't get a non-decreasing array by modify at most one element.

Solution:

  1. /**
  2.  * @param {number[]} nums
  3.  * @return {boolean}
  4.  */
  5. var checkPossibility = function(nums) {
  6.   if (nums.length === 1) return true;
  8.   let count = 0;
  10.   for (let i = 0; i < nums.length - 1; i++) {
  11.     if (nums[i] <= nums[i+1]) continue;
  13.     if (nums[i+1] - 1 < nums[i-1]) {
  14.       nums[i+1] = nums[i] + 1;
  15.     } else {
  16.       nums[i] = nums[i+1] - 1;
  17.     }
  19.     count++;  
  20.   }
  22.   return count < 2;
  23. };

Runtime: 68 ms, faster than 77.54% of JavaScript online submissions for Non-decreasing Array.