6/19/2017 - 10:03 AM

225. Implement Stack using Queues

  1. Implement Stack using Queues
class Stack(object):
    def __init__(self):
        initialize your data structure here.
        self.stack = []

    def push(self, x):
        :type x: int
        :rtype: nothing

    def pop(self):
        :rtype: nothing
        ele = self.stack[-1]
        del self.stack[-1]
        return ele

    def top(self):
        :rtype: int
        return self.stack[-1]

    def empty(self):
        :rtype: bool
        return len(self.stack) == 0

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.


  • You must use only standard operations of a queue -- which means only push to back, peek/pop from front, size, 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).