Lecture-1-2-Recursion.scala 1.96 KB
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// Copyright (c) 2020 EPITA Research and Development Laboratory
//
// Permission is hereby granted, free of charge, to any person obtaining
// a copy of this software and associated documentation
// files (the "Software"), to deal in the Software without restriction,
// including without limitation the rights to use, copy, modify, merge,
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//
// The above copyright notice and this permission notice shall be
// included in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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package lecture

object Recursion {
  def sumIntegersBySimpleRecursion(ints: List[Int]): Int = {
    ints match {
      case List() => 0
      // common variable names are also h::t or head::tail  or first::rest
      case i :: is => i + sumIntegersBySimpleRecursion(is)
    }
  }

  def sumIntegersByTailRecursion(ints: List[Int]): Int = {
    def sumRest(acc: Int, rest: List[Int]): Int = {
      rest match {
        case List() => acc
        case i :: is => sumRest(acc + i, is)
      }
    }

    sumRest(0, ints)
  }

  def sumIntegersByFold(ints: List[Int]): Int = {
    ints.fold(0)(_ + _)
  }

  def genLongList(len:Int, value:Double):List[Double] = {
    List.tabulate(len)(_ => value)
  }

  def main(argv:Array[String]):Unit = {
    val longList = List.tabulate(5673)(n => 0)
    println(s"sum = ${sumIntegersBySimpleRecursion(longList)}")
  }
}