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PrintInOrder.java
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PrintInOrder.java
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package by.andd3dfx.multithreading;
import java.util.concurrent.Semaphore;
/**
* <pre>
* <a href="https://leetcode.com/problems/print-in-order/">Task description</a>
*
* Suppose we have a class:
*
* public class Foo {
* public void first() { print("first"); }
* public void second() { print("second"); }
* public void third() { print("third"); }
* }
*
* The same instance of Foo will be passed to three different threads. Thread A will call first(), thread B will
* call second(), and thread C will call third(). Design a mechanism and modify the program to ensure that second()
* is executed after first(), and third() is executed after second().
*
* Note:
* We do not know how the threads will be scheduled in the operating system, even though the numbers in the input seem
* to imply the ordering. The input format you see is mainly to ensure our tests' comprehensiveness.
*
* Example 1:
* Input: nums = [1,2,3]
* Output: "firstsecondthird"
* Explanation: There are three threads being fired asynchronously. The input [1,2,3] means thread A calls first(),
* thread B calls second(), and thread C calls third(). "firstsecondthird" is the correct output.
*
* Example 2:
* Input: nums = [1,3,2]
* Output: "firstsecondthird"
* Explanation: The input [1,3,2] means thread A calls first(), thread B calls third(), and thread C calls second().
* "firstsecondthird" is the correct output.
*
* Constraints:
* nums is a permutation of [1, 2, 3].
*
* Initial code:
* class Foo {
* public void first(Runnable printFirst) throws InterruptedException {
* printFirst.run(); // Outputs "first". Do not change or remove this line.
* }
* public void second(Runnable printSecond) throws InterruptedException {
* printSecond.run(); // Outputs "second". Do not change or remove this line.
* }
* public void third(Runnable printThird) throws InterruptedException {
* printThird.run(); // Outputs "third". Do not change or remove this line.
* }
* }
* </pre>
*
* @see <a href="https://youtu.be/UTmv-H2xc9Y">Video solution</a>
*/
public class PrintInOrder {
private Semaphore semaphore2 = new Semaphore(0);
private Semaphore semaphore3 = new Semaphore(0);
public void first(Runnable printFirst) throws InterruptedException {
printFirst.run(); // Outputs "first". Do not change or remove this line.
semaphore2.release();
}
public void second(Runnable printSecond) throws InterruptedException {
semaphore2.acquire();
printSecond.run(); // Outputs "second". Do not change or remove this line.
semaphore3.release();
}
public void third(Runnable printThird) throws InterruptedException {
semaphore3.acquire();
printThird.run(); // Outputs "third". Do not change or remove this line.
}
}