题目：原题链接（简单）
解法时间复杂度空间复杂度执行用时Ans 1 (Python)––52ms (66.97%)Ans 2 (Python)Ans 3 (Python)LeetCode的Python执行用时随缘，只要时间复杂度没有明显差异，执行用时一般都在同一个量级，仅作参考意义。
解法一（使用threading.Lock实现）：
from threading import Lock class Foo: def __init__(self): self.firstJobDone = Lock() self.secondJobDone = Lock() self.firstJobDone.acquire() self.secondJobDone.acquire() def first(self, printFirst: 'Callable[[], None]') -> None: printFirst() self.firstJobDone.release() def second(self, printSecond: 'Callable[[], None]') -> None: with self.firstJobDone: printSecond() self.secondJobDone.release() def third(self, printThird: 'Callable[[], None]') -> None: with self.secondJobDone: printThird()