[Java]LeetCode1115. 交替打印FooBar | Print FooBar Alternately

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Suppose you are given the following code:

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");
    }
}
}
The same instance of FooBar will be passed to two different threads. Thread A will call foo() while thread B will call bar(). Modify the given program to output "foobar" n times.

 

Example 1:

Input: n = 1
Output: "foobar"
Explanation: There are two threads being fired asynchronously. One of them calls foo(), while the other calls bar(). "foobar" is being output 1 time.
Example 2:

Input: n = 2
Output: "foobarfoobar"
Explanation: "foobar" is being output 2 times.

---

咱們提供一個類：

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");
    }
}
}
兩個不一樣的線程將會共用一個 FooBar 實例。其中一個線程將會調用 foo() 方法，另外一個線程將會調用 bar() 方法。

請設計修改程序，以確保 "foobar" 被輸出 n 次。

 

示例 1:

輸入: n = 1
輸出: "foobar"
解釋: 這裏有兩個線程被異步啓動。其中一個調用 foo() 方法, 另外一個調用 bar() 方法，"foobar" 將被輸出一次。
示例 2:

輸入: n = 2
輸出: "foobarfoobar"
解釋: "foobar" 將被輸出兩次。

---

15ms

 1 import java.util.concurrent.locks.Condition;
 2 import java.util.concurrent.locks.Lock;
 3 import java.util.concurrent.locks.ReentrantLock;
 4 
 5 class FooBar {
 6     private int n;
 7     private boolean fooFlag;
 8     private boolean barFlag;
 9     private Lock lock;
10     private Condition fooCondition;
11     private Condition barCondition;
12 
13     public FooBar(int n) {
14         this.n = n;
15         this.fooFlag = false;
16         this.barFlag = true;
17         this.lock = new ReentrantLock();
18         this.fooCondition = lock.newCondition();
19         this.barCondition = lock.newCondition();
20     }
21 
22     public void foo(Runnable printFoo) throws InterruptedException {
23         for (int i = 0; i < n; i++) {
24             lock.lock();
25 
26             try {
27                 while (fooFlag) {
28                     fooCondition.await();
29                 }
30 
31                 /**
32                  * printFoo.run() outputs "foo". Do not change or remove this line.
33                  */
34                 printFoo.run();
35                 fooFlag = true;
36                 barFlag = false;
37                 barCondition.signal();
38             } finally {
39                 lock.unlock();
40             }
41         }
42     }
43 
44     public void bar(Runnable printBar) throws InterruptedException {
45         for (int i = 0; i < n; i++) {
46             lock.lock();
47 
48             try {
49                 while (barFlag) {
50                     barCondition.await();
51                 }
52 
53                 /**
54                  * printBar.run() outputs "bar". Do not change or remove this line.
55                  */
56                 printBar.run();
57                 barFlag = true;
58                 fooFlag = false;
59                 fooCondition.signal();
60             } finally {
61                 lock.unlock();
62             }
63         }
64     }
65 }

---

16ms

 1 import java.util.concurrent.Semaphore;
 2 
 3 class FooBar {
 4     private int n;
 5     private Semaphore semaphore = new Semaphore(1);
 6     private Semaphore semaphore2 = new Semaphore(0);
 7     public FooBar(int n) {
 8         this.n = n;
 9     }
10 
11     public void foo(Runnable printFoo) throws InterruptedException {
12         
13         for (int i = 0; i < n; i++) {
14             semaphore.acquire();
15             // printFoo.run() outputs "foo". Do not change or remove this line.
16             printFoo.run();
17             semaphore2.release();
18         }
19     }
20 
21     public void bar(Runnable printBar) throws InterruptedException {
22         
23         for (int i = 0; i < n; i++) {
24             semaphore2.acquire();
25             // printBar.run() outputs "bar". Do not change or remove this line.
26             printBar.run();
27             semaphore.release();
28         }
29     }
30 }

---

24ms

 1 class FooBar {
 2     private int n;
 3     private static final Object LOCK = new Object();
 4     public FooBar(int n) {
 5         this.n = n;
 6     }
 7 
 8     public void foo(Runnable printFoo) throws InterruptedException {
 9         for (int i = 0; i < n; i++) {
10             synchronized (LOCK) {
11                 LOCK.notify();
12                 printFoo.run();
13                 LOCK.wait();
14             }
15         }
16     }
17 
18     public void bar(Runnable printBar) throws InterruptedException {
19         for (int i = 0; i < n; i++) {
20             synchronized (LOCK) {
21                 LOCK.notify();
22                 printBar.run();
23                 if (i < n - 1) {
24                     LOCK.wait();
25                 }
26             }
27         }
28     }
29 }