leetcode1115-交替打印FooBar

原题

我们提供一个类:

class FooBar {
  public void foo() {
    for (int i = 0; i < n; i++) {
      print("foo");
    }
  }

  public void bar() {
    for (int i = 0; i < n; i++) {
      print("bar");
    }
  }
}

两个不同的线程将会共用一个 FooBar 实例。其中一个线程将会调用 foo() 方法,另一个线程将会调用 bar() 方法。

请设计修改程序,以确保 "foobar" 被输出 n 次。

示例 1:

输入: n = 1
输出: "foobar"
解释: 这里有两个线程被异步启动。其中一个调用 foo() 方法, 另一个调用 bar() 方法,"foobar" 将被输出一次。

示例 2:

输入: n = 2
输出: "foobarfoobar"
解释: "foobar" 将被输出两次。

解法

思想

wait_notify, await_signal

代码

wait_notify

class FooBar {
    boolean flag = false;
    private int n;

    public FooBar(int n) {
        this.n = n;
    }

    public void foo(Runnable printFoo) throws InterruptedException {
        synchronized(this){
            for (int i = 0; i < n; i++) {
                while(flag) this.wait(); 
                // printFoo.run() outputs "foo". Do not change or remove this line.
                printFoo.run();
                flag = true;
                this.notifyAll();
            }
        }
    }

    public void bar(Runnable printBar) throws InterruptedException {
        synchronized(this){
            for (int i = 0; i < n; i++) {
                while(!flag) this.wait(); 
                // printBar.run() outputs "bar". Do not change or remove this line.
                printBar.run();
                flag = false;
                this.notifyAll();
            }
        }
    }
}

await_signal

class FooBar {
    private int n;
    boolean flag;
    ReentrantLock lock;
    Condition condition;
    public FooBar(int n) {
        this.n = n;
        lock = new ReentrantLock();
        condition = lock.newCondition();
    }

    public void foo(Runnable printFoo) throws InterruptedException {
        lock.lock();
        try{
            for (int i = 0; i < n; i++) {
                while(flag) condition.await(); 
                // printFoo.run() outputs "foo". Do not change or remove this line.
                printFoo.run();
                flag = true;
                condition.signalAll();
            }
        }finally{
            lock.unlock();
        }
    }

    public void bar(Runnable printBar) throws InterruptedException {
        lock.lock();
        try{
            for (int i = 0; i < n; i++) {
                while(!flag) condition.await(); 
                // printBar.run() outputs "bar". Do not change or remove this line.
                printBar.run();
                flag = false;
                condition.signalAll();
            }
        }finally{
            lock.unlock();
        }
    }
}

原创文章,作者:彭晨涛,如若转载,请注明出处:https://www.codetool.top/article/leetcode1115-%e4%ba%a4%e6%9b%bf%e6%89%93%e5%8d%b0foobar/

发表回复

登录后才能评论