# Leetcode - Implement Queue using Stacks Solution

Implement a first in first out (FIFO) queue using only two stacks. The implemented queue should support all the functions of a normal queue (`push`

, `peek`

, `pop`

, and `empty`

).

Implement the `MyQueue`

class:

`void push(int x)`

Pushes element x to the back of the queue.`int pop()`

Removes the element from the front of the queue and returns it.`int peek()`

Returns the element at the front of the queue.`boolean empty()`

Returns`true`

if the queue is empty,`false`

otherwise.

**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, the stack may not be supported natively. You may simulate a stack using a list or deque (double-ended queue) as long as you use only a stack's standard operations.

**Follow-up:** Can you implement the queue such that each operation is **amortized** `O(1)`

time complexity? In other words, performing `n`

operations will take overall `O(n)`

time even if one of those operations may take longer.

**Example 1:**

```
Input
["MyQueue", "push", "push", "peek", "pop", "empty"]
[[], [1], [2], [], [], []]
Output
[null, null, null, 1, 1, false]
Explanation
MyQueue myQueue = new MyQueue();
myQueue.push(1); // queue is: [1]
myQueue.push(2); // queue is: [1, 2] (leftmost is front of the queue)
myQueue.peek(); // return 1
myQueue.pop(); // return 1, queue is [2]
myQueue.empty(); // return false
```

**Constraints:**

`1 <= x <= 9`

- At most
`100`

calls will be made to`push`

,`pop`

,`peek`

, and`empty`

. - All the calls to
`pop`

and`peek`

are valid.

## Solution in python

```
class MyQueue:
def __init__(self):
self.queue = deque()
def push(self, x: int) -> None:
self.queue.append(x)
def pop(self) -> int:
return self.queue.popleft()
def peek(self) -> int:
return self.queue[0]
def empty(self) -> bool:
return False if self.queue else 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()
```