[LeetCode] Rotate Array

Posted 2020-10-08 immjc

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.

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.

反转字符串，使用三步反转法，详见：[Algorithm] Reverse String

class Solution {
public:
    void rotate(vector<int>& nums, int k) {
        if (nums.empty())
            return;
        int n = nums.size();
        while (k > n) {
            k %= n;    
        }
        rotateCore(nums, 0, n - 1);
        rotateCore(nums, 0, k - 1);
        rotateCore(nums, k, n - 1);
    }
    void rotateCore(vector<int>& nums, int left, int right) {
        while (left < right) 
            swap(nums[left++], nums[right--]);
    }
};
// 19 ms