Suppose you are given the following code:
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:
- Thread A will call
zero()which should only output 0’s. - Thread B will call
even()which should only ouput even numbers. - 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
C++
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// 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(); } } }; |
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