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Implement a stack using two queues

Golu Rawat answered on August 24, 2022 Popularity 10/10 Helpfulness 1/10

answer Implement a stack using two queues

Implement a stack using two queues

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/* Java Program to implement a stack
using two queue */
import java.util.*;
 
class Stack {
    Queue<Integer> q1 = new LinkedList<>(), q2 = new LinkedList<>();
 
    void remove()
    {
        if (q1.isEmpty())
            return;
 
        // Leave one element in q1 and
        // push others in q2.
        while (q1.size() != 1) {
            q2.add(q1.peek());
            q1.remove();
        }
 
        // Pop the only left element
        // from q1
        q1.remove();
 
        // swap the names of two queues
        Queue<Integer> q = q1;
        q1 = q2;
        q2 = q;
    }
 
    void add(int x)
    {
        q1.add(x);
    }
 
    int top()
    {
        if (q1.isEmpty())
            return -1;
 
        while (q1.size() != 1) {
            q2.add(q1.peek());
            q1.remove();
        }
 
        // last pushed element
        int temp = q1.peek();
 
        // to empty the auxiliary queue after
        // last operation
        q1.remove();
 
        // push last element to q2
        q2.add(temp);
 
        // swap the two queues names
        Queue<Integer> q = q1;
        q1 = q2;
        q2 = q;
        return temp;
    }
 
    int size()
    {
        return q1.size();
    }
 
    // Driver code
    public static void main(String[] args)
    {
        Stack s = new Stack();
        s.add(1);
        s.add(2);
        s.add(3);
        s.add(4);
 
        System.out.println("current size: " + s.size());
        System.out.println(s.top());
        s.remove();
        System.out.println(s.top());
        s.remove();
        System.out.println(s.top());
        System.out.println("current size: " + s.size());
    }
}
 
// This code is contributed by Princi Singh

Popularity 10/10 Helpfulness 1/10 Language whatever

Source: www.geeksforgeeks.org

Tags: stack using whatever

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Contributed on Aug 24 2022

Golu Rawat

0 Answers Avg Quality 2/10

Implement a stack using two queues

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