Rotate Array
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?
Related problem: Reverse Words in a String II
Solution
Can we do this in O(1) space and in O(n) time? The following solution does.
Assuming we are given {1,2,3,4,5,6} and order 2. The basic idea is:
- Divide the array two parts: 1,2,3,4 and 5, 6
- Rotate first part: 4,3,2,1,5,6
- Rotate second part: 4,3,2,1,6,5
- Rotate the whole array: 5,6,1,2,3,4
Code
public class Solution {
public void rotate(int[] nums, int k) {
int len = nums.length;
k %= len;
reverse(nums, 0, len-1);
reverse(nums, 0, k-1);
reverse(nums, k, len-1);
}
public void reverse(int[] nums, int l, int r) {
while (l <= r) {
int temp = nums[l];
nums[l] = nums[r];
nums[r] = temp;
l++;
r--;
}
}
}