# 225. Implement Stack using Queues

[https://leetcode.com/problems/implement-stack-using-queues/description/](https://leetcode.com/problems/implement-stack-using-queues/description/)

## solution

```python
class MyStack:
    def __init__(self):
        self.q1 = []
        self.q2 = []

    def push(self, x: int) -> None:
        self.q1.append(x)

    def pop(self) -> int:
        if self.empty():
            return None

        for i in range(len(self.q1) - 1):
            self.q2.append(self.q1.pop(0))
        self.q1, self.q2 = self.q2, self.q1
        return self.q2.pop(0)

    def top(self) -> int:
        if self.q1:
            return self.q1[-1]

    def empty(self) -> bool:
        if self.q1:
            return False
        else:
            return True
```

时间复杂度：O()\
空间复杂度：O()
