Rotate.java

package normal; /**
 * @program JavaBooks
 * @description: 189.旋转数组
 * @author: mf
 * @create: 2019/11/04 15:46
 */

import java.util.Arrays;

/**
 * 题目：https://leetcode-cn.com/problems/rotate-array/
 * 难度:easy
 */

/*
输入: [1,2,3,4,5,6,7] 和 k = 3
输出: [5,6,7,1,2,3,4]
解释:
向右旋转 1 步: [7,1,2,3,4,5,6]
向右旋转 2 步: [6,7,1,2,3,4,5]
向右旋转 3 步: [5,6,7,1,2,3,4]


输入: [-1,-100,3,99] 和 k = 2
输出: [3,99,-1,-100]
解释:
向右旋转 1 步: [99,-1,-100,3]
向右旋转 2 步: [3,99,-1,-100]
 */
public class Rotate {
    public static void main(String[] args) {
        int[] nums = {1,2,3,4,5,6,7};
        int k = 3;
        rotate2(nums, k);
        System.out.println(Arrays.toString(nums));
    }
    // 双重循环 时间复杂度：O(kn) 空间复杂度:O(1)
    private static void rotate(int[] nums, int k) {
        int n = nums.length;
        k %= n;
        for (int i = 0; i < k; i++) {
            int temp = nums[n - 1];
            for (int j = n - 1; j > 0; j--) {
                nums[j] = nums[j - 1];
            }
            nums[0] = temp;
        }
    }
    // 翻转 时间复杂度：O(n) 空间复杂度:O(1)
    private static void rotate2(int[] nums, int k) {
        int n = nums.length;
        k %= n;
        reverse(nums, 0, n - 1);
        reverse(nums, 0, k - 1);
        reverse(nums, k, n - 1);

    }
    private static void reverse(int[] nums, int start, int end) {
        while (start < end) {
            int temp = nums[start];
            nums[start++] = nums[end];
            nums[end--] = temp;
        }
    }
}