fizzBuzzMultithreaded.cpp

// Source: https://leetcode.com/problems/fizz-buzz-multithreaded/
// Author: Miao Zhang
// Date:   2021-04-16

class Semaphore {
public:
  Semaphore (int count = 0): count_(count) {}
 
  inline void notify() {
    unique_lock<std::mutex> lock(mtx_);
    count_++;
    cv_.notify_one();
  }
 
  inline void wait() {
    unique_lock<std::mutex> lock(mtx_);
    while (count_ == 0) cv_.wait(lock);
    count_--;
  }
 
private:
  mutex mtx_;
  condition_variable cv_;
  int count_;
};


class FizzBuzz {
private:
    int n;
    Semaphore sn;
    Semaphore s3;
    Semaphore s5;
    Semaphore s15;

public:
    FizzBuzz(int n): n(n), sn(1), s3(0), s5(0), s15(0) {
    }

    // printFizz() outputs "fizz".
    void fizz(function<void()> printFizz) {
        for (int i = 3; i <= n; i += 3) {
            if (i % 5 == 0) continue;
            s3.wait();
            printFizz();      
            sn.notify();
        }
    }

    // printBuzz() outputs "buzz".
    void buzz(function<void()> printBuzz) {
        for (int i = 5; i <= n; i += 5) {
            if (i % 3 == 0) continue;
            s5.wait();
            printBuzz();      
            sn.notify();
        }
    }

    // printFizzBuzz() outputs "fizzbuzz".
	void fizzbuzz(function<void()> printFizzBuzz) {
        for (int i = 15; i <= n; i += 15) {
            s15.wait();
            printFizzBuzz();      
            sn.notify();
        }
    }

    // printNumber(x) outputs "x", where x is an integer.
    void number(function<void(int)> printNumber) {
        for (int i = 1; i <= n; i++) {
            if (i % 15 == 0) { s15.notify(); sn.wait(); }
            else if (i % 5 == 0) { s5.notify(); sn.wait(); }
            else if (i % 3 == 0) { s3.notify(); sn.wait(); }
            else { printNumber(i); } 
        }   
    }
};