> For the complete documentation index, see [llms.txt](https://gl01.gitbook.io/gfg-editorials/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://gl01.gitbook.io/gfg-editorials/2024/01-2024-jan-11/12-reverse-first-k-elements-of-queue.md).

# 12. Reverse First K elements of Queue

The problem can be found at the following link: [Question Link](https://www.geeksforgeeks.org/problems/reverse-first-k-elements-of-queue/1)

![](https://badgen.net/badge/Level/Easy/green)

## My Approach

* Initialize an empty stack temp and an empty queue ans.
* Loop through the first 'k' elements of the input queue 'q'.
  * Push each element onto the stack 'temp'.
  * Remove each element from the front of the queue using q.pop().
* Pop elements from the stack and enqueue them into the 'ans' queue, effectively reversing the order of the first 'k' elements.
* Enqueue the remaining elements from the original queue 'q' into the 'ans' queue, maintaining their original order.
* Return the modified 'ans' queue.

## Time and Auxiliary Space Complexity

* **Time Complexity**: `O(N)`, where N is the total number of elements in the queue
* **Auxiliary Space Complexity**: `O(N)`, where N is the total number of elements in the queue

## Code (C++)

```cpp
class Solution
{
    public:
    queue<int> modifyQueue(queue<int> q, int k)
    {
        stack<int>temp;
        queue<int>ans;
        for (int i=0;i<k;i++)
        {
            temp.push(q.front());
            q.pop();
        }
        while (!temp.empty())
        {
            ans.push(temp.top());
            temp.pop();
        }
        while (!q.empty())
        {
            ans.push(q.front());
            q.pop();
        }
        return ans;
    }
};
```

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