189. Rotate Array

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.

此题想出来的第一个解题思路是整体旋转一次，然后0-（k-1）旋转一次，后面的数组元素再旋转一次，代码如下：

public class Solution {

    public void rotate(int[] nums, int k) {

        k = k%(nums.length);

        rotatehelper(nums,0,nums.length-1);

        rotatehelper(nums,0,k-1);

        rotatehelper(nums,k,nums.length-1);

    }

    public void rotatehelper(int[] nums,int left,int right){

        int l = left;

        int r = right;

        while(l<r){

            int temp = nums[l];

            nums[l] = nums[r];

            nums[r] = temp;

            l++;

            r--;

        }

    }

}

第二种方法是把原来的数组元素放到排好序的新数组里面，然后新数组的值赋值回原数组里面，代码如下：

public class Solution {

    public void rotate(int[] nums, int k) {

        int[] num = new int[nums.length];

        for(int i=0;i<nums.length;i++){

            num[(i+k)%(nums.length)] = nums[i];

        }

        for(int i=0;i<num.length;i++){

            nums[i] = num[i];

        }

    }

}