Scala 99 Problems

Scala99Problems

//P01
def last(ls: List[Int]): Int = ls match {
   case le::Nil => le
   case _::tail => last(tail)
   case _ => throw new IllegalArgumentException
}

//P02
def penultimate(ls: List[Int]): Int = ls match {
   case pmate::_::Nil => pmate
   case _::tail => penultimate(tail)
   case _ => throw new IllegalArgumentException
}

//P03
def nth(i:Int, l:List[Int]):Int = (i,l) match {
   case(0,h::_) => h
   case(k,_::tail) if k>=0 => nth(k-1,tail)
   case _ => throw new IllegalArgumentException
}

//P04
def length(l:List[Int]) = {
   def lengthAcc(l:List[Int],acc:Int):Int = l match {
      case Nil => acc
      case _::tail => lengthAcc(tail,acc+1)
   }
   lengthAcc(l,0)
}

def lengthFunc(l:List[Int]):Int = l.foldLeft(0){(acc,_)=>acc+1}

//P05
def reverse(l:List[Int]):List[Int]= {
   def reverseAcc(l:List[Int],acc:List[Int]):List[Int] = l match {
      case Nil => acc
      case h::tail => reverseAcc(tail, h::acc)
   }
   reverseAcc(l,List())
}

def reverseFunc(l:List[Int]):List[Int] = l.foldLeft(List[Int]()){ (acc, v) => v::acc}