Scala - Find duplicates in list using pattern matching and recursion

Question

I am trying to solve a beginner problem but can't reach the solution:

If any duplicates in list, return true, else false. Empty lists considered.

def duplicates(a: List[Int]): Boolean = {
  case Nil => false
  case x :: xs =>
    if(xs.contains(x)) true else false
}

But this doesn't work. And it's not recursive. It's just something where I wanted to start but I'm stuck. Please kindly help and try to avoid non-beginner solutions if reasonable.

Knows Not Much · Accepted Answer · 2018-11-05 21:16:10Z

1

You need to call your function recursively. So if xs doesn't contain x, then call the function but with the remaining list.

def duplicates(a: List[Int]): Boolean = a match {
  case Nil => false
  case x :: xs =>
    if(xs.contains(x)) true else duplicates(xs)
}

answered Nov 5, 2018 at 21:16

Knows Not Much

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3 Comments

Luis Miguel Mejía Suárez Over a year ago

Sorry, I downvoted by mistake and can't upvote unless an edit is made.

ktii Over a year ago

It works, and I understand the duplicates(xs) in the end. But I don't understand why this 'a match' has to be there and why it resulted in error with 'false' in the end instead of duplicats(xs). Even if in the last case it would have been incorrect result, I still see it should have worked. Where I'm thinking wrong?

ktii Over a year ago

Ok, understood 'match' now.

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