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86 lines
2.5 KiB
Markdown
86 lines
2.5 KiB
Markdown
# [1752. Check if Array Is Sorted and Rotated](https://leetcode.com/problems/check-if-array-is-sorted-and-rotated/)
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## 题目
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Given an array `nums`, return `true` *if the array was originally sorted in non-decreasing order, then rotated **some** number of positions (including zero)*. Otherwise, return `false`.
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There may be **duplicates** in the original array.
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**Note:** An array `A` rotated by `x` positions results in an array `B` of the same length such that `A[i] == B[(i+x) % A.length]`, where `%` is the modulo operation.
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**Example 1:**
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```
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Input: nums = [3,4,5,1,2]
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Output: true
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Explanation: [1,2,3,4,5] is the original sorted array.
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You can rotate the array by x = 3 positions to begin on the the element of value 3: [3,4,5,1,2].
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```
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**Example 2:**
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```
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Input: nums = [2,1,3,4]
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Output: false
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Explanation: There is no sorted array once rotated that can make nums.
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```
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**Example 3:**
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```
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Input: nums = [1,2,3]
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Output: true
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Explanation: [1,2,3] is the original sorted array.
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You can rotate the array by x = 0 positions (i.e. no rotation) to make nums.
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```
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**Example 4:**
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```
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Input: nums = [1,1,1]
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Output: true
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Explanation: [1,1,1] is the original sorted array.
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You can rotate any number of positions to make nums.
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```
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**Example 5:**
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```
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Input: nums = [2,1]
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Output: true
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Explanation: [1,2] is the original sorted array.
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You can rotate the array by x = 5 positions to begin on the element of value 2: [2,1].
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```
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**Constraints:**
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- `1 <= nums.length <= 100`
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- `1 <= nums[i] <= 100`
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## 题目大意
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给你一个数组 nums 。nums 的源数组中，所有元素与 nums 相同，但按非递减顺序排列。如果 nums 能够由源数组轮转若干位置（包括 0 个位置）得到，则返回 true ；否则，返回 false 。源数组中可能存在 重复项 。
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## 解题思路
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- 简单题。从头扫描一遍数组，找出相邻两个元素递减的数对。如果递减的数对只有 1 个，则有可能是轮转得来的，超过 1 个，则返回 false。题干里面还提到可能有多个重复元素，针对这一情况还需要判断一下 `nums[0]` 和 `nums[len(nums)-1]` 。如果是相同元素，`nums[0] < nums[len(nums)-1]`，并且数组中间还存在一对递减的数对，这时候也是 false。判断好上述这 2 种情况，本题得解。
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## 代码
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```go
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package leetcode
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func check(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 || nums[0] < nums[len(nums)-1] {
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return false
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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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``` |