665. Non-decreasing Array

package LeetCode_665

/**
 * 665. Non-decreasing Array
 * https://leetcode.com/problems/non-decreasing-array/
 * 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. 1 <= n <= 10 ^ 4
2. - 10 ^ 5 <= nums[i] <= 10 ^ 5
 * */
class Solution {
    /*
    * solution: check current number with previous two number, Time:O(n), Space:O(1)
    * */
    fun checkPossibility(nums: IntArray): Boolean {
        var count = 0
        var previous = nums[0]
        for (i in 1 until nums.size) {
            //current less than prev, we need update
            if (nums[i] < previous) {
                if (count++ >= 1) {
                    return false
                }
            }
            //if current less then previous two number, keep compare last previous, else update previous
            if (i != 1 && nums[i] < previous && nums[i] < nums[i - 2]) {
                continue
            }
            previous = nums[i]
        }
        return true
    }
}