1116. 打印零与奇偶数

题目描述

假设有这么一个类：

class ZeroEvenOdd {
  public ZeroEvenOdd(int n) { ... }      // 构造函数public void zero(printNumber) { ... }  // 仅打印出 0public void even(printNumber) { ... }  // 仅打印出 偶数public void odd(printNumber) { ... }   // 仅打印出 奇数
}

相同的一个 ZeroEvenOdd 类实例将会传递给三个不同的线程：

线程 A 将调用 zero()，它只输出 0 。
线程 B 将调用 even()，它只输出偶数。
线程 C 将调用 odd()，它只输出奇数。

每个线程都有一个 printNumber 方法来输出一个整数。请修改给出的代码以输出整数序列 010203040506... ，其中序列的长度必须为 2n。

示例 1：

输入：n = 2
输出："0102"
说明：三条线程异步执行，其中一个调用 zero()，另一个线程调用 even()，最后一个线程调用odd()。正确的输出为 "0102"。

示例 2：

输入：n = 5
输出："0102030405"

解法

题目要求交替打印，先打印0，再打印偶数，最后打印奇数。一共打印2*n个数字。

Java

import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;class ZeroEvenOdd {private int n;private int state = 0; // 0: print zero, 1: print odd, 2: print evenprivate ReentrantLock lock = new ReentrantLock();private Condition zeroCondition = lock.newCondition();private Condition evenCondition = lock.newCondition();private Condition oddCondition = lock.newCondition();public ZeroEvenOdd(int n) {this.n = n;}// printNumber.accept(x) outputs "x", where x is an integer.public void zero(IntConsumer printNumber) throws InterruptedException {for (int i = 0; i < n; i++) {lock.lock();try {while (state != 0) {zeroCondition.await();}printNumber.accept(0);if ((i + 1) % 2 == 1) {state = 1; // next print oddoddCondition.signal();} else {state = 2; // next print evenevenCondition.signal();}} finally {lock.unlock();}}}public void even(IntConsumer printNumber) throws InterruptedException {for (int i = 2; i <= n; i += 2) {lock.lock();try {while (state != 2) {evenCondition.await();}printNumber.accept(i);state = 0; // next print zerozeroCondition.signal();} finally {lock.unlock();}}}public void odd(IntConsumer printNumber) throws InterruptedException {for (int i = 1; i <= n; i += 2) {lock.lock();try {while (state != 1) {oddCondition.await();}printNumber.accept(i);state = 0; // next print zerozeroCondition.signal();} finally {lock.unlock();}}}
}

Java

class ZeroEvenOdd {private int n;private int state = 0; // 0: print zero, 1: print odd, 2: print evenpublic ZeroEvenOdd(int n) {this.n = n;}// printNumber.accept(x) outputs "x", where x is an integer.public void zero(IntConsumer printNumber) throws InterruptedException {for (int i = 0; i < n; i++) {synchronized (this) {while (state != 0) {this.wait();}printNumber.accept(0);if ((i + 1) % 2 == 1) {state = 1; // next print odd} else {state = 2; // next print even}this.notifyAll();}}}public void even(IntConsumer printNumber) throws InterruptedException {for (int i = 2; i <= n; i += 2) {synchronized (this) {while (state != 2) {this.wait();}printNumber.accept(i);state = 0; // next print zerothis.notifyAll();}}}public void odd(IntConsumer printNumber) throws InterruptedException {for (int i = 1; i <= n; i += 2) {synchronized (this) {while (state != 1) {this.wait();}printNumber.accept(i);state = 0; // next print zerothis.notifyAll();}}}
}