LeetCode 多线程 1116. 打印零与奇偶数

Posted 2021-08-14 Alex Hub

1116. 打印零与奇偶数

Ideas

有几个线程就用几个信号量，最先开始的信号量初始化为1，其它初始化为0，然后根据条件判断实现同步。

多线程的问题好多都是：锁自己，解锁别人。

Code

from threading import Semaphore


class ZeroEvenOdd:
    def __init__(self, n):
        self.n = n + 1
        self.zero_lock = Semaphore(1)
        self.even_lock = Semaphore(0)
        self.odd_lock = Semaphore(0)

    # printNumber(x) outputs "x", where x is an integer.
    def zero(self, printNumber: 'Callable[[int], None]') -> None:
        for i in range(1, self.n):
            self.zero_lock.acquire()
            printNumber(0)
            if i % 2 == 1:
                self.odd_lock.release()
            else:
                self.even_lock.release()

    def even(self, printNumber: 'Callable[[int], None]') -> None:
        for i in range(2, self.n, 2):
            self.even_lock.acquire()
            printNumber(i)
            self.zero_lock.release()

    def odd(self, printNumber: 'Callable[[int], None]') -> None:
        for i in range(1, self.n, 2):
            self.odd_lock.acquire()
            printNumber(i)
            self.zero_lock.release()