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59 lines
1.8 KiB
Markdown
59 lines
1.8 KiB
Markdown
# [665. Non-decreasing Array](https://leetcode.com/problems/non-decreasing-array/)
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## 题目
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Given an array `nums` with `n` integers, your task is to check if it could become non-decreasing by modifying **at most one element**.
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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`).
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**Example 1:**
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```
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Input: nums = [4,2,3]
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Output: true
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Explanation: You could modify the first 4 to 1 to get a non-decreasing array.
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```
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**Example 2:**
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```
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Input: nums = [4,2,1]
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Output: false
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Explanation: You can't get a non-decreasing array by modify at most one element.
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```
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**Constraints:**
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- `n == nums.length`
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- `1 <= n <= 104`
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- `-10^5 <= nums[i] <= 10^5`
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## 题目大意
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给你一个长度为 n 的整数数组，请你判断在 最多 改变 1 个元素的情况下，该数组能否变成一个非递减数列。我们是这样定义一个非递减数列的： 对于数组中任意的 i (0 <= i <= n-2)，总满足 nums[i] <= nums[i + 1]。
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## 解题思路
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- 简单题。循环扫描数组，找到 `nums[i] > nums[i+1]` 这种递减组合。一旦这种组合超过 2 组，直接返回 false。找到第一组递减组合，需要手动调节一次。如果 `nums[i + 1] < nums[i - 1]`，就算交换 `nums[i+1]` 和 `nums[i]`，交换结束，`nums[i - 1]` 仍然可能大于 `nums[i + 1]`，不满足题意。正确的做法应该是让较小的那个数变大，即 `nums[i + 1] = nums[i]`。两个元素相等满足非递减的要求。
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## 代码
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```go
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package leetcode
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func checkPossibility(nums []int) bool {
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count := 0
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for i := 0; i < len(nums)-1; i++ {
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if nums[i] > nums[i+1] {
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count++
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if count > 1 {
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return false
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}
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if i > 0 && nums[i+1] < nums[i-1] {
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nums[i+1] = nums[i]
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}
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}
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}
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return true
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}
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``` |