Question

我注意到currentTimeMillis方法工作不正常。即使应用在30秒内计算出一个阶乘，但差异始终为3。

object Main extends App {

  def factorial(n: BigInt) = {
    val start = currentTimeMillis()
    @tailrec
    def rec(acc: BigInt, n: BigInt): BigInt = if (n <= 1) acc else rec(n * acc, n - 1)

    val fac: BigInt = rec(1, n)
    val end = currentTimeMillis()

    ((end - start) / 1000, fac)
  }

  val res = factorial(100000)
  println(s"Get ${res._2} \n in ${res._1} seconds")

}

我的代码有什么问题？为什么会返回错误的结果？

Answer 1

您的代码没有任何问题。对我来说，输出似乎是正确的：

import java.lang.System.currentTimeMillis
import scala.annotation.tailrec

object Main extends App {
  def factorial(n: BigInt) = {
    val start = currentTimeMillis()
    @tailrec
    def rec(acc: BigInt, n: BigInt): BigInt = if (n <= 1) acc else rec(n * acc, n - 1)

    val fac: BigInt = rec(1, n)
    val end = currentTimeMillis()

    ((end - start) / 1000, fac)
  }

  def printTimeForFactorial(n: BigInt) = {
    val res = factorial(n)
    println(s"Factorial of ${n} took ${res._1} seconds")
  }

  printTimeForFactorial(1)
  printTimeForFactorial(1000)
  printTimeForFactorial(10000)
  printTimeForFactorial(50000)
  printTimeForFactorial(100000)
  printTimeForFactorial(110000)
  printTimeForFactorial(120000)
}

打印

Factorial of 1 took 0 seconds
Factorial of 1000 took 0 seconds
Factorial of 10000 took 0 seconds
Factorial of 50000 took 1 seconds
Factorial of 100000 took 5 seconds
Factorial of 110000 took 6 seconds
Factorial of 120000 took 7 seconds

System.currentTimeMillis在Scala中无法正常工作

1 个答案: