查找给定数字中每个数字的乘积

Question

在scala中，我需要编写一种方法来查找给定数字中每个数字的乘积。我有以下片段。

  def productDigits(number: Int): Int = {
    def helper(current: Int, accumulator: Int): Int = {
      current match {
        case current if current < 10 => accumulator * current
        case _ => helper(current / 10, accumulator * (current % 10))
      }
    }
    helper(number, 1)
  }

还有更好的方法吗？

Answer 1

这里是OP的递归解决方案与Luis的一线相比的基准。

正在执行

sbt "jmh:run -i 10 -wi 10 -f 2 -t 1 bench.So59652263"

where

@State(Scope.Benchmark)
@BenchmarkMode(Array(Mode.Throughput))
class So59652263 {
  def _dexter2305(number: Int): Int = {
    def helper(current: Int, accumulator: Int): Int = {
      current match {
        case current if current < 10 => accumulator * current
        case _ => helper(current / 10, accumulator * (current % 10))
      }
    }
    helper(number, 1)
  }

  def _luis(number: Int): Int = number.toString.map(_.asDigit).product

  val num: Int = (math.random * 100000000).toInt
  @Benchmark def dexter2305: Int = _dexter2305(num)
  @Benchmark def luis: Int = _luis(num)
}

给予

[info] So59652263.dexter2305  thrpt   20  89093066.408 ± 1825286.801  ops/s
[info] So59652263.luis        thrpt   20  11585098.230 ±  272966.526  ops/s

我们看到递归解决方案的吞吐量似乎比单行代码高7倍。

---

number为String而不是Int时的基准测试>

@State(Scope.Benchmark)
@BenchmarkMode(Array(Mode.Throughput))
class So59652263 {
  def _dexter2305(number: String): Int = {
    def helper(current: Int, accumulator: Int): Int = {
      current match {
        case current if current < 10 => accumulator * current
        case _ => helper(current / 10, accumulator * (current % 10))
      }
    }
    helper(number.toInt, 1)
  }

  def _luis(number: String): Int = number.map(_.asDigit).product

  val num: String = (math.random * 100000000).toInt.toString
  @Benchmark def dexter2305: Int = _dexter2305(num)
  @Benchmark def luis: Int = _luis(num)
}
给予

[info] Benchmark               Mode  Cnt         Score         Error  Units
[info] So59652263.dexter2305  thrpt   20  36237007.844 ± 1631349.975  ops/s
[info] So59652263.luis        thrpt   20  13975984.042 ± 1890083.941  ops/s
我们看到递归解仍然具有较高的吞吐量，但是比number为Int时小2.5倍。