Leetcode Rotate Array

Given an array, rotate the array to the right by k steps, where k is non-negative.

Example 1:

Input: nums = [1,2,3,4,5,6,7], 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: nums = [-1,-100,3,99], 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]


Constraints:

- 1 <= nums.length <= 105
- -231 <= nums[i] <= 231 - 1
- 0 <= k <= 105


Solution

Here are the working code in C#

Solution 1: Time O(n), Space O(n)

public class Solution {
public void Rotate(int[] nums, int k)
{
var res = new int[nums.Length];
for (int i = 0; i < nums.Length; i++)
{
var newPos = (i + k) % nums.Length;
res[newPos] = nums[i];
}

for (int i = 0; i < res.Length; i++)
{
nums[i] = res[i];
}
}
}


Solution 2: Time O(n), Space O(1). Set k=k%n, reverse the whole array, then reverse the array from 0 to k-1 and then from k to n-1

public class Solution
{
public void Rotate(int[] nums, int k)
{
k %= nums.Length;
Reverse(nums, 0, nums.Length - 1);
Reverse(nums, 0, k - 1);
Reverse(nums, k, nums.Length - 1);
}

public void Reverse(int[] nums, int start, int end)
{
while (start < end)
{
(nums[start], nums[end]) = (nums[end], nums[start]);
start++;
end--;
}
}
}