28. Implement stack using queues

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

My Approach

This is the standard problem , In this we can create two queue and then -

1. For push operation, first we push the givem value in queue 2

2. After that we push all the value of queue 1 in queue 2 ,it will result in the first element will be present at the last of queue

3. We swap queue 1 and 2 it will result that the first element of queue is the element we just pushed for in queue 2.

Time and Auxiliary Space Complexity

• Time Complexity: O(n)

• Auxiliary Space Complexity: O(n) because we used an extra queue..

Code (C++)

class MyStack {
    queue<int> q1, q2;
public:
    MyStack() {

    }
    
    void push(int x) {
        q2.push(x);

        while(!q1.empty()){
            q2.push(q1.front());
            q1.pop();
        }

        queue<int> temp;
        temp = q1;
        q1 = q2;
        q2 = temp;

    }
    
    int pop() {
 
        int val = q1.front();
        q1.pop();
        return val;
    }
    
    int top() {
        return q1.front();
    }
    
    bool empty() {
        if(q1.empty()) return true;
        else return false;
    }
};

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