题目：

题解：

class MyQueue:def __init__(self):self.A, self.B = [], []def push(self, x: int) -> None:self.A.append(x)def pop(self) -> int:peek = self.peek()self.B.pop()return peekdef peek(self) -> int:if self.B: return self.B[-1]if not self.A: return -1# 将栈 A 的元素依次移动至栈 Bwhile self.A:self.B.append(self.A.pop())return self.B[-1]def empty(self) -> bool:return not self.A and not self.B