232.用栈实现队列

难度：简单
题目描述：

思路总结：也是瞎J8做的，还需要重新做一下。
题解一：

class MyQueue:

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

    def push(self, x: int) -> None:
        """
        Push element x to the back of queue.
        """
        self.data.append(x)

    def pop(self) -> int:
        """
        Removes the element from in front of queue and returns that element.
        """
        return self.data.pop(0)

    def peek(self) -> int:
        """
        Get the front element.
        """
        return self.data[0]

    def empty(self) -> bool:
        """
        Returns whether the queue is empty.
        """
        if len(self.data) == 0:return True
        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()

题解一结果：

题解二：（双栈）
两个栈，一个存放先进先出的序列，另一个作为辅助。

class MyQueue:

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

    def push(self, x: int) -> None:
        """
        Push element x to the back of queue.
        """
        while self.data:
            self.helper.append(self.data.pop())
        self.helper.append(x)
        while self.helper:
            self.data.append(self.helper.pop())
        
    def pop(self) -> int:
        """
        Removes the element from in front of queue and returns that element.
        """
        res = self.data.pop()
        return res

    def peek(self) -> int:
        """
        Get the front element.
        """
        head = self.data.pop()
        self.data.append(head)
        return head

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

题解二结果：