DAY16P1.md

Implement Queue using Stacks

---

• Question:

Implement a first in first out (FIFO) queue using only two stacks. The implemented queue should support all the functions of a normal queue (push, peek, pop, and empty).

---

• Example:

Input ["MyQueue", "push", "push", "peek", "pop", "empty"] [[], [1], [2], [], [], []]

Output [null, null, null, 1, 1, false]

---

• Solution:

Code :

class MyQueue {

    Stack<Integer> og;
    Stack<Integer> temp;
    int top;
    
    public MyQueue() {
        og = new Stack();
        temp = new Stack();
    }
    
    public void push(int x) {
        if(og.empty())
            top = x;
        og.push(x);
    }
    
    public int pop() {
        while(og.size() != 1)
        {
            temp.push(og.pop());
        }
        int popped = og.pop();
        if(!temp.empty())
            top = temp.peek();
        while(!temp.empty())
        {
            og.push(temp.pop());
        }
        return popped;
    }
    
    public int peek() {
        return top;
    }
    
    public boolean empty() {
        return og.empty();
    }
}