[leetcode: Python]232. Implement Queue using Stacks

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题目：
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).

方法一：性能39ms

class MyQueue(object):

    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.queue = []


    def push(self, x):
        """
        Push element x to the back of queue.
        :type x: int
        :rtype: void
        """
        self.queue.append(x)


    def pop(self):
        """
        Removes the element from in front of queue and returns that element.
        :rtype: int
        """
        if not self.empty():
            return self.queue.pop(0)

    def peek(self):
        """
        Get the front element.
        :rtype: int
        """
        if not self.empty():
            return self.queue[0]

    def empty(self):
        """
        Returns whether the queue is empty.
        :rtype: bool
        """
        return len(self.queue) == 0


# Your MyQueue object will be instantiated and called as such:
# obj = MyQueue()
# obj.push(x)
# param_2 = obj.pop()
# param_3 = obj.peek()
# param_4 = obj.empty()

方法二：性能32ms

    def push(self, x):
        self.stack.append(x)
        self.curElements += 1
        """
        Push element x to the back of queue.
        :type x: int
        :rtype: void
        """

    def pop(self):
        res = self.stack[self.curFront]
        self.curFront += 1
        self.curElements -= 1
        return res
        """
        Removes the element from in front of queue and returns that element.
        :rtype: int
        """

    def peek(self):
        return self.stack[self.curFront]
        """
        Get the front element.
        :rtype: int
        """

    def empty(self):
        return self.curElements == 0
        """
        Returns whether the queue is empty.
        :rtype: bool
        """



# Your MyQueue object will be instantiated and called as such:
# obj = MyQueue()
# obj.push(x)
# param_2 = obj.pop()
# param_3 = obj.peek()
# param_4 = obj.empty()

本文标签： PythonLeetCodeStacksQueueimplement