leetcode:(665)Non-Decreasing Array(java)

题目描述：

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].

题目描述：

判断一个数组是否可以通过修改一个数组值变为非递减数组。

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解题思路：

在出现 nums[i] < nums[i - 1] 时，需要考虑的是应该修改数组的哪个数，使得本次修改能使 i 之前的数组成为非递减数组，并且不影响后续的操作 。优先考虑令 nums[i - 1] = nums[i]，因为如果修改 nums[i] = nums[i - 1] 的话，那么 nums[i] 这个数会变大，就有可能比 nums[i + 1] 大，从而影响了后续操作。还有一个比较特别的情况就是 nums[i] < nums[i - 2]，只修改 nums[i - 1] = nums[i] 不能使数组成为非递减数组，只能修改 nums[i] = nums[i - 1]。具体解题思路及代码如下：

package Leetcode_Github;

public class GreedyThought_NonDecreasingArray_665_1112 {
    public boolean CheckPossibility(int[] nums){
        if (nums == null || nums.length <= 1) {
            return true;
        }

        //用来记录修改数组次数
        int count = 0;
        for (int i = 1; i < nums.length && count < 2; i++) {
            //如果索引i的值比i-1的值大，进行下一次循环
            if (nums[i] >= nums[i - 1]) {
                continue;
            }

            count++;
            //如果nums[i]的值比nums[i-2]的值小，将nums[i-1]的值赋给nums[i]
            if (i >= 2 && nums[i] < nums[i - 2]) {
                nums[i] = nums[i - 1];
            } else
                //如果只是nums[i]的值小于nums[i-1],将nums[i]的值赋给nums[i-1]
                nums[i - 1] = nums[i];
        }
        //如果数组修改次数为0或者1，返回true
        return count <= 1;
    }

    public static void main(String[] args) {
        int[] array = {3, 4, 2, 3};
        GreedyThought_NonDecreasingArray_665_1112 test = new GreedyThought_NonDecreasingArray_665_1112();
        boolean result = test.CheckPossibility(array);
        System.out.println(result);
    }
}

参考：https://github.com/CyC2018/CS-Notes/blob/master/notes/Leetcode%20%E9%A2%98%E8%A7%A3.md#%E8%B4%AA%E5%BF%83%E6%80%9D%E6%83%B3

leetcode:(665)Non-Decreasing Array(java)

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