Solution to a simple Hackerrank problem: Compare the Triplets

Question

Given two equally sized arrays of integers A and B, compute the number of times A[i] > B[i] and the number of times A[i] < B[i] for each index i.

New to scala, I put together the following solution:

import scala.io.Source

object Solution {

    def main(args: Array[String]) {
        val lines = Source.stdin.getLines
        val alice = lines.next.split(" ").map(_.toInt)
        val bob = lines.next.split(" ").map(_.toInt)

        val competitions = alice zip bob
        val scoreA = competitions.count(c => c._1 > c._2)
        val scoreB = competitions.count(c => c._1 < c._2)

        printf("%d %d", scoreA, scoreB)
    }
}

I normally solve these problems using python, so I simply searched online for my usual programming constructs. I have a few questions.

• Is there a more general way to print a list of space separated integers? Currently my use of printf is limited to exactly two.
• Are there any pitfalls I'm unaware of?
• Ideas of more concise solutions without sacrificing readability?

Any other insights would be greatly appreciated!

Answer 1

You don't have to traverse the competitions array twice. The results can be collected in a tuple result after a single traversal.

val results = competitions.foldLeft((0,0)){
                             case ((aw,bw),(a,b)) => 
                               if (a>b)      (aw+1,bw) //a won
                               else if (b>a) (aw,bw+1) //b won
                               else          (aw,bw)   //tie
                           }

The tuple's elements can be accessed via indexing, results._1 and results._2, but it can be more convenient to unpack it via pattern matching.

val (scoreA, scoreB) = results

So, putting it all together, and removing the competitions step (just because you can).

val (aWins
    ,bWins) = alice.zip(bob)
                   .foldLeft((0,0)){
                      case ((aw,bw),(a,b)) =>
                        if (a>b)      (aw+1,bw)
                        else if (b>a) (aw,bw+1)
                        else          (aw,bw)
                   }

Sending the results to STDOUT is usually done via println(), either with string catenation...

println(aWins + " " + bWins)

...or with string interpolation.

println(s"$aWins $bWins")