Question

1195. Fizz Buzz Multithreaded

中文文档

Description

You have the four functions:

• printFizz that prints the word "fizz" to the console,
• printBuzz that prints the word "buzz" to the console,
• printFizzBuzz that prints the word "fizzbuzz" to the console, and
• printNumber that prints a given integer to the console.

You are given an instance of the class FizzBuzz that has four functions: fizz, buzz, fizzbuzz and number. The same instance of FizzBuzz will be passed to four different threads:

• Thread A: calls fizz() that should output the word "fizz".
• Thread B: calls buzz() that should output the word "buzz".
• Thread C: calls fizzbuzz() that should output the word "fizzbuzz".
• Thread D: calls number() that should only output the integers.

Modify the given class to output the series [1, 2, "fizz", 4, "buzz", ...] where the ith token (1-indexed) of the series is:

• "fizzbuzz" if i is divisible by 3 and 5,
• "fizz" if i is divisible by 3 and not 5,
• "buzz" if i is divisible by 5 and not 3, or
• i if i is not divisible by 3 or 5.

Implement the FizzBuzz class:

• FizzBuzz(int n) Initializes the object with the number n that represents the length of the sequence that should be printed.
• void fizz(printFizz) Calls printFizz to output "fizz".
• void buzz(printBuzz) Calls printBuzz to output "buzz".
• void fizzbuzz(printFizzBuzz) Calls printFizzBuzz to output "fizzbuzz".
• void number(printNumber) Calls printnumber to output the numbers.

 

Example 1:

Input: n = 15
Output: [1,2,"fizz",4,"buzz","fizz",7,8,"fizz","buzz",11,"fizz",13,14,"fizzbuzz"]

Example 2:

Input: n = 5
Output: [1,2,"fizz",4,"buzz"]

 

Constraints:

• 1 <= n <= 50

Solutions

Solution 1

class FizzBuzz {
  private int n;

  public FizzBuzz(int n) {
    this.n = n;
  }

  private Semaphore fSema = new Semaphore(0);
  private Semaphore bSema = new Semaphore(0);
  private Semaphore fbSema = new Semaphore(0);
  private Semaphore nSema = new Semaphore(1);

  // printFizz.run() outputs "fizz".
  public void fizz(Runnable printFizz) throws InterruptedException {
    for (int i = 3; i <= n; i = i + 3) {
      if (i % 5 != 0) {
        fSema.acquire();
        printFizz.run();
        nSema.release();
      }
    }
  }

  // printBuzz.run() outputs "buzz".
  public void buzz(Runnable printBuzz) throws InterruptedException {
    for (int i = 5; i <= n; i = i + 5) {
      if (i % 3 != 0) {
        bSema.acquire();
        printBuzz.run();
        nSema.release();
      }
    }
  }

  // printFizzBuzz.run() outputs "fizzbuzz".
  public void fizzbuzz(Runnable printFizzBuzz) throws InterruptedException {
    for (int i = 15; i <= n; i = i + 15) {
      fbSema.acquire();
      printFizzBuzz.run();
      nSema.release();
    }
  }

  // printNumber.accept(x) outputs "x", where x is an integer.
  public void number(IntConsumer printNumber) throws InterruptedException {
    for (int i = 1; i <= n; i++) {
      nSema.acquire();
      if (i % 3 == 0 && i % 5 == 0) {
        fbSema.release();
      } else if (i % 3 == 0) {
        fSema.release();
      } else if (i % 5 == 0) {
        bSema.release();
      } else {
        printNumber.accept(i);
        nSema.release();
      }
    }
  }
}

class FizzBuzz {
private:
  std::mutex mtx;
  atomic<int> index;
  int n;

  // 这里主要运用到了C++11中的RAII锁(lock_guard)的知识。
  // 需要强调的一点是，在进入循环后，要时刻不忘加入index <= n的逻辑
public:
  FizzBuzz(int n) {
    this->n = n;
    index = 1;
  }

  void fizz(function<void()> printFizz) {
    while (index <= n) {
      std::lock_guard<std::mutex> lk(mtx);
      if (0 == index % 3 && 0 != index % 5 && index <= n) {
        printFizz();
        index++;
      }
    }
  }

  void buzz(function<void()> printBuzz) {
    while (index <= n) {
      std::lock_guard<std::mutex> lk(mtx);
      if (0 == index % 5 && 0 != index % 3 && index <= n) {
        printBuzz();
        index++;
      }
    }
  }

  void fizzbuzz(function<void()> printFizzBuzz) {
    while (index <= n) {
      std::lock_guard<std::mutex> lk(mtx);
      if (0 == index % 15 && index <= n) {
        printFizzBuzz();
        index++;
      }
    }
  }

  void number(function<void(int)> printNumber) {
    while (index <= n) {
      std::lock_guard<std::mutex> lk(mtx);
      if (0 != index % 3 && 0 != index % 5 && index <= n) {
        printNumber(index);
        index++;
      }
    }
  }
};