Day 38 of 100 Days LeetCode Challenge

LeetCode Challenge #225. Implement Stack using Queues

Implement a last-in-first-out (LIFO) stack using only two queues. The implemented stack should support all the functions of a normal stack (pushtoppop, and empty).

Implement the MyStack class:

  • void push(int x) Pushes element x to the top of the stack.
  • int pop() Removes the element on the top of the stack and returns it.
  • int top() Returns the element on the top of the stack.
  • boolean empty() Returns true if the stack is empty, false otherwise.


  • You must use only standard operations of a queue, which means that only push to backpeek/pop from frontsize and is empty operations are valid.
  • Depending on your language, the queue may not be supported natively. You may simulate a queue using a list or deque (double-ended queue) as long as you use only a queue’s standard operations.


Example 1:

["MyStack", "push", "push", "top", "pop", "empty"]
[[], [1], [2], [], [], []]
[null, null, null, 2, 2, false]

MyStack myStack = new MyStack();
myStack.push(2);; // return 2
myStack.pop(); // return 2
myStack.empty(); // return False



  • 1 <= x <= 9
  • At most 100 calls will be made to pushpoptop, and empty.
  • All the calls to pop and top are valid.
Video Solution
Java Solution
					class MyStack {
    private Queue<Integer> main;
    private Queue<Integer> helper;

    public MyStack() {
        main = new LinkedList<>();
        helper = new LinkedList<>();
    public void push(int x) {
    //   moving all elements from main to helper 
    //   add x in main queue 
    //   moving all elements from helper to main

    public int pop() {
        return main.remove();
    public int top() {
        return main.peek();
    public boolean empty() {
            return true ;
            return false;

 * Your MyStack object will be instantiated and called as such:
 * MyStack obj = new MyStack();
 * obj.push(x);
 * int param_2 = obj.pop();
 * int param_3 =;
 * boolean param_4 = obj.empty();

Happy Coding with edSlash