LeetCode #189 Rotate Array
Given an array, rotate the array to the right by k steps, where k is non-negative.
Example 1:
Input: [1,2,3,4,5,6,7] and k = 3
Output: [5,6,7,1,2,3,4]
Explanation:
rotate 1 steps to the right: [7,1,2,3,4,5,6]
rotate 2 steps to the right: [6,7,1,2,3,4,5]
rotate 3 steps to the right: [5,6,7,1,2,3,4]Example 2:
Input: [-1,-100,3,99] and k = 2
Output: [3,99,-1,-100]
Explanation:
rotate 1 steps to the right: [99,-1,-100,3]
rotate 2 steps to the right: [3,99,-1,-100]Note:
- Try to come up as many solutions as you can, there are at least 3 different ways to solve this problem.
- Could you do it in-place with O(1) extra space?
Solution
Divide list into two parts, first and last. Reverse last, reverse first and reverse whole list.
Complexity
In reverse, it will take O(s/2) time for a s size slice. And we first call it with a m size slice which takes O(m/2) time. Then, O((n-m)/2) time for the second reverse and O(n/2) time for the last reverse.
Therefore, time complexity for this solution is O(m/2 + (n-m)/2 + n/2) = O(n). Because we only use in place behavior so there is only O(1) extra space.
