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 0
  public 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：

1. 线程 A 将调用 zero()，它只输出 0 。
2. 线程 B 将调用 even()，它只输出偶数。
3. 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 even
    private 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 odd
                    oddCondition.signal();
                } else {
                    state = 2; // next print even
                    evenCondition.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 zero
                zeroCondition.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 zero
                zeroCondition.signal();
            } finally {
                lock.unlock();
            }
        }
    }
}

Java

class ZeroEvenOdd {
    private int n;
    private int state = 0; // 0: print zero, 1: print odd, 2: print even

    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++) {
            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 zero
                this.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 zero
                this.notifyAll();
            }
        }
    }
}

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