Non-decreasing Array

Description

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

Solution(javascript)

/** 1. Monotone Stack 不行
 *  2. 两种可能，改当前的数或者改前一个数
 * @param {number[]} nums
 * @return {boolean}
 */
const checkPossibility = function (nums) {
  const check = (arr = []) => {
    for (let i = 1; i < nums.length; i++) {
      if (nums[i] < nums[i - 1]) {
        return false
      }
    }
    return true
  }
  for (let i = 0; i < nums.length; i++) {
    if (nums[i] < nums[i - 1]) {
      const temp = nums[i]
      nums[i] = nums[i - 1]
      if (check(nums)) {
        return true
      }
      nums[i] = temp
      nums[i - 1] = nums[i]
      return check(nums)
    }
  }
  return true
}