# Problem

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).false

# Python3

``````# 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:

def __init__(self):
"""
"""
self._data = []
self._temp_stack = []

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

def pop(self):
"""
Removes the element from in front of queue and returns that element.
:rtype: int
"""
if len(self._temp_stack) == 0:
while len(self._data) != 0:
self._temp_stack.append(self._data.pop())
return self._temp_stack.pop()

def peek(self):
"""
Get the front element.
:rtype: int
"""
if len(self._temp_stack) == 0:
while len(self._data) != 0:
self._temp_stack.append(self._data.pop())
return self._temp_stack[-1]

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

Thanks a lot.