Queue: Reverse a stack using queue

Problem Statement:

You are given a stack, reverse the stack using queue

Example:

Input: s = [1, 2, 3, 4]

Output q = [4, 3, 2, 1] 

Solution Explanation:

Solution is very simple.

First push all the element from stack to queue.

Then push from queue to stack and get the result.

Time Complexity: O(1)
Space Complexity: O(1)

Code Solution

#include <iostream>
#include <vector>
#include <queue>
#include <stack>
using namespace std;



void solution(queue<int> &q)
{

    stack<int> st;

    while (!q.empty())
    {
        st.push(q.front());
        q.pop();
    }

    while (!st.empty())
    {
        q.push(st.top());
        st.pop();
    }
}

void display(queue<int> q)
{

    while(!q.empty())
    {
        cout<<q.front()<<" ";
        q.pop();
    }
    cout<<endl;
}

int main()
{
    queue<int> q;

    for(int i=1; i<=5; i++)
    {
        q.push(i);
    }

    cout<<"Before reverse: ";
    display(q);
    
    solution(q);

    cout<<"After reverse: ";
    display(q);
}

Output

Before reverse: 1 2 3 4 5 
After reverse: 5 4 3 2 1