189. Rotate Array(两次反转)

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Pick One

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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]

Related problem: Reverse Words in a String II

 class Solution {
     public void rotate(int[] nums, int k) {
         k%=nums.length;
         if(k==0) return;

         reverce(nums,0,nums.length-1);
         reverce(nums,0,k-1);
         reverce(nums,k,nums.length-1);
     }
     private void reverce(int[] a,int i,int j){
         for(int k = 0;k <= (j-i)/2;k++){
             swap(a,i+k,j-k);
         }
     }
     private void swap(int[] a,int i ,int j){
         int temp = a[i];
         a[i] = a[j];
         a[j] = temp;
     }
 }