LeetCode 189. Rotate Array（旋转数组）

原题网址：https://leetcode.com/problems/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.

[show hint]

Related problem: Reverse Words in a String II

方法一：使用临时空间。

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

方法二：逐个向前推移，直到所有元素都在目标位置。

public class Solution {
    private int gcd(int a, int b) {
        if (a < b) {
            int t = a;
            a = b;
            b = t;
        }
        while (b > 0) {
            int t = a % b;
            a = b;
            b = t;
        }
        return a;
    }
    public void rotate(int[] nums, int k) {
        k = k % nums.length;
        int g = gcd(nums.length, k);
        int l = nums.length * k / g;
        for(int i=0; i

方法三：翻转。

public class Solution {
    private void reverse(int[] nums, int from, int to) {
        while (from < to) {
            nums[from] ^= nums[to];
            nums[to] ^= nums[from];
            nums[from] ^= nums[to];
            from ++;
            to --;
        }
    }
    public void rotate(int[] nums, int k) {
        k = k % nums.length;
        reverse(nums, 0, nums.length-k-1);
        reverse(nums, nums.length-k, nums.length-1);
        reverse(nums, 0, nums.length-1);
    }
}