Scala Recusion/Tail Recursion

Question

I'm trying to practice recursive and tail recursive functions using Scala, I've created a tail recursive function to sum the values in two lists. I'm trying to do the same with recursion too but the only way I could think of was to modify the parameter each time the method was called like tail recursion. Can you help me out?

def callTailRecursive(list1 : List[Int], list2 : List[Int]) : List[Int] = { def callHelper(list1 : List[Int], list2 : List[Int], outputList : List[Int]): List[Int] ={ if(!list1.isEmpty && !list2.isEmpty){ callHelper(list1.tail,list2.tail,outputList:+(list1.head + list2.head)) }else if(list1.isEmpty && !list2.isEmpty){ callHelper(list1,list2.tail,outputList:+(list2.head)) }else if(!list1.isEmpty && list2.isEmpty){ callHelper(list1.tail,list2,outputList:+(list1.head)) }else{ outputList } } callHelper(list1,list2,List()) } def callRecursive(n : Int, list1 : List[Int], list2 : List[Int], outputList : List[Int]): List[Int] = { }

"tail recursive" is a subset of "recursive". Every tail recursive function is, almost definitionally, a recursive function. What are you trying to do? Write a function that specifically isn't tail recursive? That sounds akin to trying to write a function with the requirement that it take at least an hour to run. You're optimizing for negative things. — Silvio Mayolo
– Silvio Mayolo, Commented Nov 11, 2021 at 1:37

jwvh · Accepted Answer · 2021-11-11 02:21:18Z

Pattern matching. It's the bee's knees.

def callRecursive(list1: List[Int], list2: List[Int]): List[Int] = (list1,list2) match { case (hd1::tl1, hd2::tl2) => (hd1+hd2) :: callRecursive(tl1, tl2) case (_, Nil) => list1 case (Nil, _) => list2 } def notRecursive(list1: List[Int], list2: List[Int]): List[Int] = list1.zipAll(list2, 0, 0).map{case (a,b) => a+b}

Collectives™ on Stack Overflow

Scala Recusion/Tail Recursion

1 Answer 1

Comments

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Related