LeetCode in Kotlin

1115. Print FooBar Alternately

Medium

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.

Constraints:

• 1 <= n <= 1000

Solution

import java.util.concurrent.Semaphore

class FooBar(private val n: Int) {
    private val fooSemaphore: Semaphore
    private val barSemaphore: Semaphore

    init {
        fooSemaphore = Semaphore(1)
        barSemaphore = Semaphore(1)
        try {
            barSemaphore.acquire()
        } catch (ignored: InterruptedException) {
            // ignored
        }
    }

    @Throws(InterruptedException::class)
    fun foo(printFoo: Runnable) {
        for (i in 0 until n) {
            fooSemaphore.acquire()
            // printFoo.run() outputs "foo". Do not change or remove this line.
            printFoo.run()
            barSemaphore.release()
        }
    }

    @Throws(InterruptedException::class)
    fun bar(printBar: Runnable) {
        for (i in 0 until n) {
            barSemaphore.acquire()
            // printBar.run() outputs "bar". Do not change or remove this line.
            printBar.run()
            fooSemaphore.release()
        }
    }
}

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