232. 用栈实现队列

232. 用栈实现队列

方法一

class MyQueue(object):

    def __init__(self):
        """
        Initialize your data structure here.
        """
        self.stack1 = []
        self.stack2 = []
        

    def push(self, x):
        """
        Push element x to the back of queue.
        :type x: int
        :rtype: void
        """
        self.stack1.append(x)
        

    def pop(self):
        """
        Removes the element from in front of queue and returns that element.
        :rtype: int
        """
        if self.stack2:
            return self.stack2.pop()
        else:
            while self.stack1:
                e = self.stack1.pop()
                self.stack2.append(e)
            return self.stack2.pop()
        

    def peek(self):
        """
        Get the front element.
        :rtype: int
        """
        if self.stack2:
            return self.stack2[len(self.stack2) - 1]
        else:
            while self.stack1:
                e = self.stack1.pop()
                self.stack2.append(e)
            return self.stack2[len(self.stack2) - 1]
        

    def empty(self):
        """
        Returns whether the queue is empty.
        :rtype: bool
        """
        if len(self.stack1) == 0 and len(self.stack2) == 0:
            return True
        else:
            return False
        


# 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()
"""

• push(x) -- 将一个元素放入队列的尾部。
• pop() -- 从队列首部移除元素。
• peek() -- 返回队列首部的元素。
• empty() -- 返回队列是否为空。

"""