665. Non-decreasing Array
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] Output: True Explanation: You could modify the first 4 to 1 to get a non-decreasing array. Example 2: Input: [4,2,1] Output: False Explanation: You can't get a non-decreasing array by modify at most one element. Note: The n belongs to [1, 10,000].
class Solution { public boolean checkPossibility(int[] nums) { if (nums == null || nums.length < 3) { return true; } int cnt = 0; for (int i = 1; i< nums.length; i++) { if (nums[i] < nums[i - 1]) { if (i < nums.length - 1 && nums[i + 1] < nums[i - 1]) { nums[i - 1] = nums[i]; cnt++; if (i - 2 >= 0 && nums[i - 2] > nums[i - 1]) { return false; } } else { nums[i] = nums[i - 1]; cnt++; } } if (cnt > 1) { return false; } } return true; } }
We can also do it without modifying the input by using a variable prev
to hold the a[i-1]
; if we have to lower a[i]
to match a[i-1]
instead of raising a[i-1]
, simply skip updating prev
;
without modified
class Solution { public boolean checkPossibility(int[] a) { int modified = 0; for (int i = 1, prev = a[0]; i < a.length; i++) { if (a[i] < prev) { if (modified++ > 0) return false; if (i - 2 >= 0 && a[i - 2] > a[i]) continue; } prev = a[i]; } return true; } }