Leetcode 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.

思路：

1. 用另一个数组存储，rotate后该数组的样子，然后再依次赋值给原数组。

public void rotate1(int[] nums, int k) {
    if (nums == null || nums.length <= 1) {
        return;
    }

    int[] rnums = new int[nums.length];
    for (int i = 0; i < nums.length; i++) {
        rnums[(i+k)%nums.length] = nums[i];
    }
    for (int i = 0; i < nums.length; i++) {
        nums[i] = rnums[i];
    }
}

2. 先reverse整个数组，然后reverse前k个，再reverse后面的部分。

public void rotate(int[] nums, int k) {
    if (nums == null || nums.length <= 1) {
        return;
    }

    //k > n or k < n
    int len = nums.length;
    k %= len;

    reverse(nums, 0, len - 1);
    reverse(nums, 0, k - 1);
    reverse(nums, k, len - 1);
}

private void reverse(int[] nums, int start, int end) {
    if (start >= end) {
        return;
    }
    while (start < end) {
        int tmp = nums[start];
        nums[start++] = nums[end];
        nums[end--] = tmp;
    }
}