LeetCode 189. Rotate Array[Easy]

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题目地址：https://leetcode.com/problems/rotate-array/

题解地址：https://leetcode.com/articles/rotate-array/

题目

Given an array, rotate the array to the right by k steps, where k is non-negative.

Follow up:

  • Try to come up as many solutions as you can, there are at least 3 different ways to solve this problem.
  • Could you do it in-place with O(1) extra space?

Example 1:

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Input: nums = [1,2,3,4,5,6,7], k = 3
Output: [5,6,7,1,2,3,4]
Explanation:
rotate 1 steps to the right: [7,1,2,3,4,5,6]
rotate 2 steps to the right: [6,7,1,2,3,4,5]
rotate 3 steps to the right: [5,6,7,1,2,3,4]

Example 2:

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Input: nums = [-1,-100,3,99], k = 2
Output: [3,99,-1,-100]
Explanation: 
rotate 1 steps to the right: [99,-1,-100,3]
rotate 2 steps to the right: [3,99,-1,-100]

Constraints:

  • 1 <= nums.length <= 2 * 10^4
  • It’s guaranteed that nums[i] fits in a 32 bit-signed integer.
  • k >= 0

解法1：蛮力法

思路

一次向右移动 1 位，移动 k 次。

代码

略

解法2：使用额外数组

思路

使用和原数组大小相同的额外数组，直接把原数组元素放置到新数组对应位置上。

代码

略

解法3：循环赋值

思路

从第一个元素开始依次向后移动，每次都先把下一个元素缓存起来，这样最终会循环到最初的位置。

代码

解法4：三次翻转

思路

整体翻转一次。

把前 k 个翻转一下。

把后 n-k 个翻转一下。

代码