189. Rotate Array

难度: Medium

题目描述

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

 

Example 1:

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:

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 <= 105
• -231 <= nums[i] <= 231 - 1
• 0 <= k <= 105

 

Follow up:

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

解题思路

代码实现

解决方案

java

class Solution {
    public void rotate(int[] nums, int k) {
        //1. k = k%nums.length;
        //2. 翻转数组
        //3. 翻转前k个元素
        //4.翻转剩下的元素
        int len = nums.length;
        int rK = k % len;
        rotateArray(nums, 0, len - 1);
        rotateArray(nums, 0, rK - 1);
        rotateArray(nums, rK, len - 1);

    }

    private void rotateArray(int[] nums, int start, int end) {
        int len = nums.length;
        if (start < 0 || end < 0 || start >= len || end >= len) {
            return;
        }
        if (start >= end) {
            return;
        }
        while (start < end) {
            int temp = nums[start];
            nums[start] = nums[end];
            nums[end] = temp;
            start++;
            end--;
        }
    }
}