[232] Implement Queue using Stacks

https://leetcode.com/problems/implement-queue-using-stacks/description/

• algorithms
• Easy (40.62%)
• Source Code: 232.implement-queue-using-stacks.py
• Total Accepted: 144.1K
• Total Submissions: 337.2K
• Testcase Example: '["MyQueue","push","push","peek","pop","empty"]\n[[],[1],[2],[],[],[]]'

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.

Example:

MyQueue queue = new MyQueue();

queue.push(1); queue.push(2);
queue.peek(); // returns 1 queue.pop(); // returns 1 queue.empty(); // returns false

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).

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: None
        """
        self.stack1.append(x)


    def pop(self):
        """
        Removes the element from in front of queue and returns that element.
        :rtype: int
        """
        if not self.stack2:
            while self.stack1:
                self.stack2.append(self.stack1.pop(-1))

        val = self.stack2.pop(-1)
        return val


    def peek(self):
        """
        Get the front element.
        :rtype: int
        """
        if not self.stack2:
            while self.stack1:
                self.stack2.append(self.stack1.pop(-1))

        val = self.stack2[-1]
        return val



    def empty(self):
        """
        Returns whether the queue is empty.
        :rtype: bool
        """
        if not self.stack1 and not self.stack2:
            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()