12. Reverse First K elements of Queue

The problem can be found at the following link: Question Link

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++)

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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