> ## Documentation Index
> Fetch the complete documentation index at: https://leetcode-py.wisl.dev/llms.txt
> Use this file to discover all available pages before exploring further.

> ## Agent Instructions
> leetcode-py is a Python LeetCode practice environment generator with one CLI: lcpy. It is not a service or platform.
> Each problem is a directory under leetcode/ with README.md, solution.py, test_solution.py, helpers.py, and playground.ipynb. lcpy gen creates them from JSON templates bundled with the package.
> Examples are backed by tests; copy them verbatim.

# Implement Stack using Queues Python Solution

> Tested Python solution for LeetCode 225 with 12 pytest cases. Generate a practice environment with lcpy.

LeetCode 225, Easy. Topics: Stack, Design, Queue. [View on LeetCode](https://leetcode.com/problems/implement-stack-using-queues/description/).

Generate this problem as a practice environment: tested reference solution, 12 [parametrized pytest cases](/practice/testing), and a playground notebook:

```bash theme={"theme":{"light":"github-light","dark":"github-dark"}}
lcpy gen -n 225   # by problem number
lcpy gen -s implement_stack_using_queues   # by problem name
```

## Problem

Implement a last-in-first-out (LIFO) stack using only two queues. The implemented stack should support all the functions of a normal stack (`push`, `top`, `pop`, and `empty`).

Implement the `MyStack` class:

* `void push(int x)` Pushes element x to the top of the stack.
* `int pop()` Removes the element on the top of the stack and returns it.
* `int top()` Returns the element on the top of the stack.
* `boolean empty()` Returns `true` if the stack is empty, `false` otherwise.

### Examples

```
Input
["MyStack", "push", "push", "top", "pop", "empty"]
[[], [1], [2], [], [], []]
Output
[null, null, null, 2, 2, false]
```

**Explanation:**

```
MyStack myStack = new MyStack();
myStack.push(1);
myStack.push(2);
myStack.top(); // return 2
myStack.pop(); // return 2
myStack.empty(); // return False
```

### Constraints

* 1 \<= x \<= 9
* At most 100 calls will be made to push, pop, top, and empty.
* All the calls to pop and top are valid.

**Notes:**

* You must use **only** standard operations of a queue, which means that only `push to back`, `peek/pop from front`, `size`, and `is empty` operations are valid.
* Depending on your language, the queue may not be supported natively. You may simulate a queue using a list or deque (double-ended queue) as long as you use only a queue's standard operations.

**Follow-up:** Can you implement the stack using only one queue?

## Solution

Reference implementation from [solution.py on GitHub](https://github.com/wislertt/leetcode-py/blob/main/leetcode/implement_stack_using_queues/solution.py), full suite in [test\_solution.py](https://github.com/wislertt/leetcode-py/blob/main/leetcode/implement_stack_using_queues/test_solution.py):

```python theme={"theme":{"light":"github-light","dark":"github-dark"}}
from collections import deque


class MyStack:
    def __init__(self) -> None:
        self.queue: deque[int] = deque()

    # Time: O(n)
    # Space: O(n)
    def push(self, x: int) -> None:
        self.queue.append(x)
        for _ in range(len(self.queue) - 1):
            self.queue.append(self.queue.popleft())

    # Time: O(1)
    # Space: O(1)
    def pop(self) -> int:
        return self.queue.popleft()

    # Time: O(1)
    # Space: O(1)
    def top(self) -> int:
        return self.queue[0]

    # Time: O(1)
    # Space: O(1)
    def empty(self) -> bool:
        return len(self.queue) == 0
```

## Complexity

| Time | Space |
| ---- | ----- |
| O(n) | O(n)  |

## Tags

[NeetCode 250](/catalog/neetcode-250), [NeetCode All](/catalog/neetcode).