[leetcode 189]Rotate Array

1 题目

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]

Hint:
Could you do it in-place with O(1) extra space?

Credits:
Special thanks to @Freezen for adding this problem and creating all test cases.

Hide Tags

 Array

 

2 思路

之前在《编程珠玑》里面看过，先旋转前部分，再选择后部分，最后旋转整个，可以得到结果，时间复杂度O（n），空间O（1），是一种比较好的算法。可以用于文本编辑器中行的移动。

3 代码

    public void rotate(int[] nums,int k) {
        int len = nums.length;
        k %= len;//很重要防止k超过len
        this.partRotate(nums, 0, len - k);
        this.partRotate(nums, len - k, len);//至于为什么不是len － k － 1与下面的实现有关吧
        this.partRotate(nums, 0, len);
    }
    
    public int[] partRotate(int[] nums, int head, int rear) {
        int temp = 0;
        
        for (int i = 0; i < (rear - head) / 2; i++) {
            temp = nums[head + i];
            nums[head + i] = nums[rear - i - 1];
            nums[rear - i - 1] = temp;
        }
        return nums;
    }