力扣上的一道题，三个线程按照顺序分别打印出来one、tow、three：

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class Foot {
    private val flag:AtomicInteger = AtomicInteger(0)
    @Throws(InterruptedException::class)
    fun first(printFirst: Runnable) {
        // printFirst.run() outputs "first". Do not change or remove this line.
        printFirst.run()
        flag.incrementAndGet()
    }

    @Throws(InterruptedException::class)
    fun second(printSecond: Runnable) {
        while (flag.get() != 1) {
        }
        // printSecond.run() outputs "second". Do not change or remove this line.
        printSecond.run()
        flag.incrementAndGet()
    }

    @Throws(InterruptedException::class)
    fun third(printThird: Runnable) {
        while (flag.get() != 2) {
        }
        // printThird.run() outputs "third". Do not change or remove this line.
        printThird.run()
        flag.incrementAndGet()
    }

    internal class PrintRunnable(private val text: String) : Runnable {
        override fun run() {
            println(text)
        }

    }

}
fun main(){
    val foot = Foot()
    thread {
        val tow = Foot.PrintRunnable("tow")
        foot.second(tow)
    }
    thread {
        val three = Foot.PrintRunnable("three")
        foot.third(three)
    }
    thread {
        val one = Foot.PrintRunnable("one")
        foot.first(one)
    }
}