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PrintZeroEvenOdd.md

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Suppose you are given the following code:

class ZeroEvenOdd {
  public ZeroEvenOdd(int n) { ... }      // constructor
  public void zero(printNumber) { ... }  // only output 0's
  public void even(printNumber) { ... }  // only output even numbers
  public void odd(printNumber) { ... }   // only output odd numbers
}

The same instance of ZeroEvenOdd will be passed to three different threads:

  1. Thread A will call zero() which should only output 0's.
  2. Thread B will call even() which should only ouput even numbers.
  3. Thread C will call odd() which should only output odd numbers.

Each of the thread is given a printNumber method to output an integer. Modify the given program to output the series 010203040506... where the length of the series must be 2n.

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"

来源：力扣（LeetCode） 链接：https://leetcode-cn.com/problems/print-zero-even-odd 著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。

解析

多线程顺序打印0-1-0-2。

可以使用信号通知。

zero运行时：

打印even： zero 通知even

打印odd： zero通知odd

odd或even运行时：

全部都需要通知zero

代码

import java.util.concurrent.Semaphore;
class ZeroEvenOdd {
    private int n;
    Semaphore zero,o,e;
    public ZeroEvenOdd(int n) {
        this.n = n;
        zero = new Semaphore(1);
        o = new Semaphore(0);
        e = new Semaphore(0);
        
    }

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

    public void even(IntConsumer printNumber) throws InterruptedException {
    for (int i = 2; i <= n; i += 2) {
        e.acquire();
        printNumber.accept(i);
        zero.release();
      }
    }

    public void odd(IntConsumer printNumber) throws InterruptedException {
    for (int i = 1; i <= n; i += 2) {
        o.acquire();
        printNumber.accept(i);
        zero.release();
      }
    }
}

解析2

还可以使用wati/notifyAll()来发送信号

设置zero和eo两个变量

zero = true代表通知zero等待

eo 表示开始打印奇偶数。e为偶数，o表示奇数

代码

class ZeroEvenOdd {
    private int n;
    private boolean zero;// 打印0
    private boolean eo;// 打印偶数或者奇数
    
    public ZeroEvenOdd(int n) {
        this.n = n;
    }

    // printNumber.accept(x) outputs "x", where x is an integer.
    public void zero(IntConsumer printNumber) throws InterruptedException {
        synchronized(this){
            for(int i = 0;i < n;i++){
                while(zero){
                this.wait();
                }
                printNumber.accept(0);
                zero = true;
                this.notifyAll();
            } 
        }
    }
    
    public void odd(IntConsumer printNumber) throws InterruptedException {
        for(int i = 1;i <= n;i += 2){
            synchronized(this){
              	// zero运行完毕，eo=false 表示开始打印奇数
                while(!(zero==true&&eo==false)){
                    this.wait();
                }
                printNumber.accept(i);
              	// 通知zero开始运行
                zero = false;
                // 通知偶数可以打印
                eo = true;
                this.notifyAll();
            }
        }
    }
    
    public void even(IntConsumer printNumber) throws InterruptedException {
        for(int i = 2;i <= n;i += 2){
            synchronized(this){
              	// zero运行完毕，eo=true，开始打印偶数
                while(!(zero==true&&eo==true)){
                    this.wait();
                }
                printNumber.accept(i);
               // 通知zero开始运行 
                zero = false;
              	// 通知奇数可以打印
                eo = false;
                this.notifyAll();
            }
        }
    }
}