Implement the following operations of a stack using queues.

  • push(x) — Push element x onto stack.
  • pop() — Removes the element on top of the stack.
  • top() — Get the top element.
  • empty() — Return whether the stack is empty.

Example:

MyStack stack = new MyStack();

stack.push(1);
stack.push(2);  
stack.top();   // returns 2
stack.pop();   // returns 2
stack.empty(); // returns false

Notes:

  • You must use only standard operations of a queue — which means only push to backpeek/pop from frontsize, and is empty operations are valid.
  • Depending on your language, queue may not be supported natively. You may simulate a queue by using a list or deque (double-ended queue), as long as you use only standard operations of a queue.
  • You may assume that all operations are valid (for example, no pop or top operations will be called on an empty stack).

Solution

public class MyStack {

    Queue queue;
    /** Initialize your data structure here. */
    public MyStack() {
        queue = new Queue();
    }
    
    /** Push element x onto stack. */
    public void Push(int x) {
        queue.Enqueue(x);
        for(int i=0;i<queue.Count-1;i++)
        {
            queue.Enqueue(queue.Dequeue());
        }
    }
    
    /** Removes the element on top of the stack and returns that element. */
    public int Pop() {
        return (int)(queue.Dequeue());
    }
    
    /** Get the top element. */
    public int Top() {
        return (int)(queue.Peek());
    }
    
    /** Returns whether the stack is empty. */
    public bool Empty() {
        return queue.Count == 0;
    }
}

/**
 * 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 = obj.Top();
 * bool param_4 = obj.Empty();
 */