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?
Related problem: Reverse Words in a String II
Credits:
Special thanks to @Freezen for adding this problem and creating all test cases.
分析
数组旋转问题。
给定一个序列和一个整数，要求将序列元素右旋k位。题目不难，但是需要注意的一点是k值可能大于序列长度，所以，旋转之前先求k对序列长度size的余数即可。
该题目一个简单的解决方法是三次反转：
- 将序列中（0 ， size-k-1）元素反转；
- 将序列中（size-k , size-1）元素反转；
将全序列（0，size-1）反转；
即可完成要求！
AC代码
class Solution {
public:
void rotate(vector<int>& nums, int k) {
if (nums.empty())
return;
int size = nums.size();
//确定最终右旋元素个数
k %= size;
vector<int>::iterator beg = nums.begin();
//旋转0~(size-k) (size-k , size);
reverse(beg, beg + size - k);
reverse(beg + size - k, nums.end());
//最后一次全部反转，即可完成
reverse(beg, nums.end());
}
};