_665_NondecreasingArray.java

package array;

/**
 * 
 * Problem:
 *
 * 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]. Solution:
 * 
 */
public class _665_NondecreasingArray {
	public boolean checkPossibility(int[] nums) {
		if (nums == null || nums.length == 0) {
			return false;
		}
		boolean dec = false;
		int peak = 0;
		for (int i = 0; i < nums.length - 1; i++) {
			if (nums[i] > nums[i + 1]) {
				if (dec) {
					return false;
				} else {
					peak = i;
					dec = true;
				}
			}
		}
		// modify the element in peak
		if (peak == 0 || nums[peak - 1] <= nums[peak + 1]) {
			return true;
		}
		// modify the element in peak + 1
		if (peak + 1 == nums.length - 1 || nums[peak] <= nums[peak + 2]) {
			return true;
		}
		return false;
	}
}