189. Rotate Array

QUESTION

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.

THOUGHT

这个方法是july在他的书中提到的方法，先把前k-n个元素旋转，再把最后k元素旋转，最后旋转整个数组，即可得到最后的结果。

CODE

public class Solution {
    public void rotate(int[] nums, int k) {
        int n = nums.length;
        k = k % n;
       reverse(nums,0,n - k -1);
       reverse(nums,n - k,n -1);
       reverse(nums,0,n - 1);
    }
    public void reverse(int[] arr,int start,int end){
        int temp = 0;
        while(start < end){
            temp = arr[start];
            arr[start] = arr[end];
            arr[end] = temp;
            start++;
            end--;
        }
    }
}

result

time complexity is max(O(n-k),O(K)),space complexity is O(1);