Implement stack using queue

// Implement stack using queue - easy - 07/08/2023

// Approach 1 - two queues - push - O(1), pop O(n) 
class MyStack {
    Queue<Integer> q1;
    Queue<Integer> q2 ;

    public MyStack() {
        q1 = new LinkedList<>();
        q2 = new LinkedList<>();
    }
    private int top; 
    public void push(int x) {
        top = x;
        q1.add(x);
    }
    
    public int pop() {
        
        while(q1.size() > 1){
            top = q1.remove();
            q2.add(top);
        }

        int res = q1.remove();
        while(!q2.isEmpty()){
            q1.add(q2.remove());
        }
        return res;
    }
    
    public int top() {      
        return top;
    }
    
    public boolean empty() {
        return q1.isEmpty();
    }
}

// Approach 2 - push O(n), pop O(1)

class MyStack {
    Queue<Integer> q1;
    Queue<Integer> q2 ;

    public MyStack() {
        q1 = new LinkedList<>();
        q2 = new LinkedList<>();
    }
    private int top; 
    public void push(int x) {
        top = x;
        q2.add(x);
        while(!q1.isEmpty()){
            q2.add(q1.remove());
        }
        Queue<Integer> temp = q1;
        q1 = q2;
        q2 = temp;
    }
    
    public int pop() {
        int res = q1.remove();
        if(!q1.isEmpty()){
            top = q1.peek();
        }
        return res;
    }
    
    public int top() {      
        return top;
    }
    
    public boolean empty() {
        return q1.isEmpty();
    }
}

// Approach 3 - one queue Push O(n), pop O(1)

class MyStack {
    Queue<Integer> q;

    public MyStack() {
        q = new LinkedList<>();
    }
     
    public void push(int x) {
       
        q.add(x);
        int size = q.size();

        while(size-- > 1){
            q.add(q.remove());
        }
    }
    
    public int pop() {
        
        return q.remove();
    }
    
    public int top() {      
        return q.peek();
    }
    
    public boolean empty() {
        return q.isEmpty();
    }
}