【LeetCode】189. Rotate Array

Difficulty:easy

 More:【目录】LeetCode Java实现

Description

https://leetcode.com/problems/rotate-array/

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

Example 1:

Input: [1,2,3,4,5,6,7] and 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: [-1,-100,3,99] and 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]

Note:

• 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?

Intuition

rotate the array for three times

Solution

    public void rotate(int[] nums, int k) {
        if(nums==null || nums.length<=0 || k==nums.length)
            return;
        k%=nums.length;
        reverse(nums, 0, nums.length-1);
        reverse(nums, 0, k-1);
        reverse(nums, k, nums.length-1);
    }
    
    public void reverse(int[] nums, int i, int j){
        while(i<j){
            nums[i]=nums[i]+nums[j];
            nums[j]=nums[i]-nums[j];
            nums[i]=nums[i]-nums[j];
            i++;
            j--;
        }
    }

　　

Complexity

Time complexity : O(n)

Space complexity : O(1)

 More:【目录】LeetCode Java实现