Comments on: Scala: Code Kata #2 – Karate Chop – Array Slicing Attempt

By: Alan Kent

Alan Kent — Wed, 28 Jul 2010 05:35:55 +0000

Doesn’t slice() return a copy of the sub-array (and so would be slow)? Should it be using .view(offset,len) instead? (Or did slice() change in Scala 2.8 so it used to be fine, but now slice() returns a copy so view() should be used instead?)

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By: Mark Needham

Mark Needham — Wed, 14 Oct 2009 13:30:56 +0000

@Raph – I really like that last bit of your solution where you pattern match on the recursive call, very cool.

I’m thinking of maybe trying this kata again and trying to make the tests pass as I go rather than hacking in the edge cases at the end to see what it comes up with.

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By: Raphael Speyer

Raphael Speyer — Wed, 14 Oct 2009 12:58:39 +0000

Oops, last post was killed by the angle brackets. I’ll try again, but in any case I put the code here: http://gist.github.com/210041

def chop(needle : Int, haystack : Array[Int]) : Int = {
if (haystack.length == 0) return -1
val midPoint = haystack.length / 2
val midValue = haystack(midPoint)

if (midValue == needle)
midPoint
else if (needle < midValue)
chop(needle, haystack.slice(0, midPoint))
else
chop(needle, haystack.slice(midPoint + 1, haystack.length)) match {
case -1 => -1
case index => midPoint + 1 + index
}
}

By: Raphael Speyer

Raphael Speyer — Wed, 14 Oct 2009 12:51:54 +0000

What about this?

def chop(needle : Int, haystack : Array[Int]) : Int = {
if (haystack.length == 0) return -1
val midPoint = haystack.length / 2
val midValue = haystack(midPoint)

if (midValue == needle)
midPoint
else if (needle -1
case index => midPoint + 1 + index
}
}

You can add the midPoint to the found index as the results are being returned up the call stack, rather than passing it as an argument on the way down.