Print Zero Even Odd

Desicription

Suppose you are given the following code:

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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 threads 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:

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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:

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Input: n = 5
Output: "0102030405"

Solution

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class ZeroEvenOdd {
private:
int n_;
int index_ = 1;
std::mutex mutex_{};
std::condition_variable condition_variable_{};

bool is_zero_ = true;

public:
ZeroEvenOdd(int n) {
this->n_ = n;
}

// printNumber(x) outputs "x", where x is an integer.
void zero(const std::function<void(int)>& printNumber) {
while(index_ <= n_) {
std::unique_lock unique_lock_{mutex_};
condition_variable_.wait(unique_lock_, [&](){return is_zero_;});
if(index_ > n_) {
is_zero_ = false;
condition_variable_.notify_all();
return ;
}
printNumber(0);
is_zero_ = false;
condition_variable_.notify_all();
}
}

void even(const std::function<void(int)>& printNumber) {
while(index_ <= n_) {
std::unique_lock unique_lock_{mutex_};
condition_variable_.wait(unique_lock_, [&](){return !is_zero_ && (index_ % 2 == 0);});
if(index_ > n_) {
condition_variable_.notify_all();
return ;
}
printNumber(index_++);
is_zero_ = true;
condition_variable_.notify_all();
}
}

void odd(const std::function<void(int)>& printNumber) {
while(index_ <= n_) {
std::unique_lock unique_lock_{mutex_};
condition_variable_.wait(unique_lock_, [&](){return !is_zero_ && (index_ % 2 == 1);});
if(index_ > n_) {
condition_variable_.notify_all();
return ;
}
printNumber(index_++);
is_zero_ = true;
condition_variable_.notify_all();
}
}
};