class ZeroEvenOdd {
  public ZeroEvenOdd(int n) { ... }      // constructor
  public void zero(printNumber) { ... }  // only output 0's
  public void even(printNumber) { ... }  // only output even numbers
  public void odd(printNumber) { ... }   // only output odd numbers
}

The same instance of ZeroEvenOdd will be passed to three different threads:

1. Thread A will call zero() which should only output 0’s.
2. Thread B will call even() which should only ouput even numbers.
3. Thread C will call odd() which should only output odd numbers.

Each of the thread is given a printNumber method to output an integer. Modify the given program to output the series 010203040506… where the length of the series must be 2n.

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"

Solution: Mutex

// Author: Huahua, 40 ms / 9 MB
class ZeroEvenOdd {
private:
  int x;
  int n;
  mutex m_zero_;
  mutex m_odd_;
  mutex m_even_;
public:
    ZeroEvenOdd(int n) {
      this->n = n;
      this->x = 1;
      m_odd_.lock();
      m_even_.lock();
    }

    // printNumber(x) outputs "x", where x is an integer.
    void zero(function<void(int)> printNumber) {
      for (int i = 0; i < n; ++i) {
        m_zero_.lock();
        printNumber(0);
        if (i % 2 == 0) {
          m_odd_.unlock();
        } else {
          m_even_.unlock();
        }
      }
    }

    void even(function<void(int)> printNumber) {
      for (int i = 2; i <= n; i += 2) {
        m_even_.lock();
        printNumber(i);
        m_zero_.unlock();
      }
    }

    void odd(function<void(int)> printNumber) {
      for (int i = 1; i <= n; i += 2) {
        m_odd_.lock();
        printNumber(i);
        m_zero_.unlock();      
      }
    }
};

The post 花花酱 LeetCode 1116. Print Zero Even Odd appeared first on Huahua's Tech Road.