problem4.py

## Problem 1: (https://leetcode.com/problems/implement-queue-using-stacks/)

class MyQueue:

    def __init__(self):
        self.in_stack = []
        self.out_stack = []

    def push(self, x: int) -> None:
        self.in_stack.append(x)

    def pop(self) -> int:
        if self.out_stack:
            return self.out_stack.pop()
        while self.in_stack:
            self.out_stack.append(self.in_stack.pop())
        return self.out_stack.pop()

    def peek(self) -> int:
        if self.out_stack:
            return self.out_stack[-1]
        if self.in_stack:
            return self.in_stack[0]
        return -1

    def empty(self) -> bool:
        if self.in_stack or self.out_stack:
            return False
        return True


# 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()