189. Rotate Array java solutions

Posted 2020-08-03 Miller1991

Rotate an array of n elements to the right by k steps.

For example, with n = 7 and k = 3, the array [1,2,3,4,5,6,7] is rotated to [5,6,7,1,2,3,4].

Note:
Try to come up as many solutions as you can, there are at least 3 different ways to solve this problem.

[show hint]

Hint:
Could you do it in-place with O(1) extra space?

Related problem: Reverse Words in a String II

Credits:
Special thanks to @Freezen for adding this problem and creating all test cases.

 1 public class Solution {
 2     public void rotate(int[] nums, int k) {
 3         int[] tmp = new int[k];
 4         int len = nums.length;
 5         k %= len;//处理k大于数组长度的情况
 6         for(int i = 0; i < k; i++){
 7             tmp[i] = nums[len-k+i];
 8         }
 9         len--;
10         for(int i = len-k; i>= 0; i--){
11             nums[len--] = nums[i];
12         }
13         for(int i = 0; i < k; i++){
14             nums[i] = tmp[i];
15         }
16     }
17 }

解法二将数组0~len-1 逆置一次，0~k-1逆置一次，k~len-1逆置一次，即可得答案：

 1 public class Solution {
 2     public void rotate(int[] nums, int k) {
 3         int len = nums.length;
 4         k %= len;
 5         reverse(nums,0,len-1);
 6         reverse(nums,0,k-1);
 7         reverse(nums,k,len-1);
 8     }
 9     
10     public void reverse(int[] nums,int s, int e){
11         while(s <= e){
12             int tmp = nums[s];
13             nums[s] = nums[e];
14             nums[e] = tmp;
15             s++;
16             e--;
17         }
18     }
19 }