1116. Print Zero Even Odd

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Problem

You have a function printNumber that can be called with an integer parameter and prints it to the console.

• For example, calling printNumber(7) prints 7 to the console.

You are given an instance of the class ZeroEvenOdd that has three functions: zero, even, and odd. The same instance of ZeroEvenOdd will be passed to three different threads:

• Thread A: calls zero() that should only output 0’s.
• Thread B: calls even() that should only output even numbers.
• Thread C: calls odd() that should only output odd numbers.

Modify the given class to output the series “010203040506…” where the length of the series must be 2n.

Implement the ZeroEvenOdd class:

• ZeroEvenOdd(int n) Initializes the object with the number n that represents the numbers that should be printed.
• void zero(printNumber) Calls printNumber to output one zero.
• void even(printNumber) Calls printNumber to output one even number.
• void odd(printNumber) Calls printNumber to output one odd number.

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"

Code

class ZeroEvenOdd {
    int n;
    
    Semaphore semaphoreEven, semaphoreOdd, semaphoreZero;
    
    public ZeroEvenOdd(int n) {
        this.n = n;
        
        semaphoreZero = new Semaphore(1);
        semaphoreEven = new Semaphore(0);
        semaphoreOdd = new Semaphore(0);
    }

    // printNumber.accept(x) outputs "x", where x is an integer.
    public void zero(IntConsumer printNumber) throws InterruptedException {
        int numTimes = this.n;
        boolean printOdd = true;
        
        for(int i = 0; i < numTimes; i++){
            semaphoreZero.acquire();
			
            printNumber.accept(0);

            //print the next number
            if(printOdd)
                semaphoreOdd.release();
            else
                semaphoreEven.release();
            
            printOdd = !printOdd;   //flip it!
        }
    }

    public void even(IntConsumer printNumber) throws InterruptedException {
        int numTimes = this.n / 2;
        
        int nextEvenNum = 2;
        for(int i = 0; i < numTimes; i++){
            semaphoreEven.acquire();
            
            printNumber.accept(nextEvenNum);
            nextEvenNum += 2;
            
            semaphoreZero.release();
        }
    }

    public void odd(IntConsumer printNumber) throws InterruptedException {
        int numTimes = (int)Math.ceil((double)this.n / 2);
        
        int nextOdd = 1;
        for(int i = 0; i < numTimes; i++){
            semaphoreOdd.acquire();
            
            printNumber.accept(nextOdd);
            nextOdd += 2;
            
            semaphoreZero.release();
        }
    }
}