1116. Print Zero Even Odd

題目敘述

You have a function printNumber that can be called with an integer parameter and prints it to the console.

• For example, calling printNumber(7) prints 7 to the console.

You are given an instance of the class ZeroEvenOdd that has three functions: zero, even, and odd. The same instance of ZeroEvenOdd will be passed to three different threads:

• Thread A: calls zero() that should only output 0's.
• Thread B: calls even() that should only output even numbers.
• Thread C: calls odd() that should only output odd numbers.

Modify the given class to output the series "010203040506..." where the length of the series must be 2n.

Implement the ZeroEvenOdd class:

• ZeroEvenOdd(int n) Initializes the object with the number n that represents the numbers that should be printed.
• void zero(printNumber) Calls printNumber to output one zero.
• void even(printNumber) Calls printNumber to output one even number.
• void odd(printNumber) Calls printNumber to output one odd number.

Example 1:

Input: n = 2
Output: "0102"
Explanation: There are three threads being fired asynchronously. One of them calls zero(), the other calls even(), and the last one calls odd(). "0102" is the correct output.

Example 2:

Input: n = 5
Output: "0102030405"

Constraints:

• 1 <= n <= 1000

題目翻譯

這題的條件是，會有三個 method，分別是 zero, even, odd。會給一個參數 n，然後需要依序從 1 印到 n，但是在每個數字前都還要先印出 0。如果是印出 0 則要執行 zero，印出偶數需要使用 even，奇數則要使用 odd。

解法解析

類似上一題 1115 一樣，使用 for-loop 去處理不同 method 的執行時機。每次 even 或 odd 執行完後，都回到 zero 的狀態。然後在 zero 的 method 中去判斷下次要執行的是 odd 或 even。

程式範例

Python

from threading import Lock


class ZeroEvenOdd:
    def __init__(self, n):
        self.n = n

        self.zero_mutex = Lock()
        self.odd_mutex = Lock()
        self.even_mutex = Lock()

        self.even_mutex.acquire()
        self.odd_mutex.acquire()

    # printNumber(x) outputs "x", where x is an integer.
    def zero(self, printNumber: 'Callable[[int], None]') -> None:
        for i in range(self.n):
            self.zero_mutex.acquire()

            printNumber(0)

            if (i % 2) == 0:
                self.even_mutex.release()
            else:
                self.odd_mutex.release()

    def even(self, printNumber: 'Callable[[int], None]') -> None:
        for i in range(2, self.n + 1, 2):
            self.odd_mutex.acquire()
            printNumber(i)
            self.zero_mutex.release()
        self.odd_mutex.release()

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