# 189 Rotate Array

Rotate an array ofnelements to the right byksteps.

For example, withn= 7 andk= 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.

**Solution 1 (Extra Space, O(n)):** Hash to the location in the array the corresponds with its its rotated position.

```cpp
void rotate(vector<int>& nums, int k) 
{
    vector<int> r_nums(nums.size());

    for (int i = 0; i < nums.size(); i++) {
        int rotate_hash = (i + k) % nums.size();
        r_nums[rotate_hash] = nums[i];
    }
    nums = r_nums;
}

int main()
{
    vector<int> nums = { 1,2,3,4,5,6,7 };
    rotate(nums, 3);

    print(nums);
}
```

**Solution 2 (Constant Space, O(n)):** Reverse the array entirely, and the reverse two segments divided at k.

```
Example:

Input
nums: 1 2 3 4 5 6 7
k   : 3

rev :         7 6 5 4 3 2 1
rev(0, k) :   5 6 7 4 3 2 1
rev(k, end) : 5 6 7 1 2 3 4
```

```cpp
void rotate(vector<int>& nums, int k)
{
    k = k % nums.size();

    reverse(nums.begin(), nums.end());
    reverse(nums.begin(), nums.begin() + k);
    reverse(nums.begin() + k, nums.end());
}

int main()
{
    vector<int> nums = { 1,2,3,4,5,6,7 };
    rotate(nums, 3);
    print(nums);
}
```


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