LeetCode-in-Java

1116. Print Zero Even Odd

Medium

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”

Constraints:

• 1 <= n <= 1000

Solution

import java.util.concurrent.Semaphore;
import java.util.function.IntConsumer;

@SuppressWarnings({"java:S2142", "java:S2583"})
public class ZeroEvenOdd {
    private int n;

    private final Semaphore zeroSemaphore = new Semaphore(1);
    private final Semaphore oddSemaphore = new Semaphore(1);
    private final Semaphore evenSemaphore = new Semaphore(1);

    public ZeroEvenOdd(int n) {
        this.n = n;
        try {
            oddSemaphore.acquire();
            evenSemaphore.acquire();
        } catch (InterruptedException ignored) {
            // ignored
        }
    }

    // printNumber.accept(x) outputs "x", where x is an integer.
    public void zero(IntConsumer printNumber) throws InterruptedException {
        for (int i = 1; i <= n; i++) {
            zeroSemaphore.acquire();
            printNumber.accept(0);
            if (i % 2 == 0) {
                oddSemaphore.release();
            } else {
                evenSemaphore.release();
            }
        }
        oddSemaphore.release();
        evenSemaphore.release();
    }

    public void odd(IntConsumer printNumber) throws InterruptedException {
        for (int i = 1; i <= n; i += 2) {
            evenSemaphore.acquire();
            if (i > n) {
                zeroSemaphore.release();
                evenSemaphore.release();
                break;
            }
            printNumber.accept(i);
            zeroSemaphore.release();
        }
    }

    public void even(IntConsumer printNumber) throws InterruptedException {
        for (int i = 2; i <= n; i += 2) {
            oddSemaphore.acquire();
            if (i > n) {
                zeroSemaphore.release();
                oddSemaphore.release();
                break;
            }
            printNumber.accept(i);
            zeroSemaphore.release();
        }
    }
}

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