moonlightshadow123
6/19/2017 - 9:49 AM

232. Implement Queue using Stacks

  1. Implement Queue using Stacks
solution.py
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class Queue(object):
    def __init__(self):
        """
        initialize your data structure here.
        """
        self.queue = []

    def push(self, x):
        """
        :type x: int
        :rtype: nothing
        """
        self.queue.append(x)

    def pop(self):
        """
        :rtype: nothing
        """
        ele = self.queue[0]
        del self.queue[0]
        return ele
        

    def peek(self):
        """
        :rtype: int
        """
        ele = self.queue[0]
        return ele

    def empty(self):
        """
        :rtype: bool
        """
        return len(self.queue) == 0
232-Implement-Queue-using-Stacks.md
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https://leetcode.com/problems/implement-queue-using-stacks/#/description

Implement the following operations of a queue using stacks.

  • push(x) -- Push element x to the back of queue.
  • pop() -- Removes the element from in front of queue.
  • peek() -- Get the front element.
  • empty() -- Return whether the queue is empty.

Notes:

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