Hi how can I take elements between two index in a collection kotlinlang #getting-started

Hi, how can I take elements between two index in a collection? For example, I have a list of 5 elements and I want to take the second to the fourth elements of this list.

menegatti

12/13/2017, 1:34 PM

https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.collections/-list/sub-list.html

yourList.subList(1, 4)

(toIndex is exclusive)

karelpeeters

12/13/2017, 1:36 PM

Also keep in mind that if you're doing this on a

MutableList

and you mutate the resulting sublist the original will change too.

GauthierPLM

12/13/2017, 1:39 PM

Thank you !

Is there anyway to optimize this (giving that “tour” is a Set

val path = listOf(tour.toList().let {
             it.subList(index, it.size)
        }, tour.toList().subList(0, index)).flatten()

diesieben07

12/13/2017, 1:58 PM

I mean... if I understand that correctly, that should be the same as just

tour.toList()

, considering you are making the sub lists 0 to index and then index to size, which will span the whole list. Right?

menegatti

12/13/2017, 2:14 PM

it’s actually reversing the list, e.g

listOf(1, 2, 3,4)

becomes

listOf(3, 4, 1, 2)

karelpeeters

12/13/2017, 2:16 PM

Revering lists, hmm, I wonder why you'd need that. @GauthierPLM come join us at #advent-of-code!

diesieben07

12/13/2017, 2:16 PM

Right, so add a

asReversed

at the end.

GauthierPLM

12/13/2017, 2:55 PM

@karelpeeters i’m trying to solve a TSP problem using the Greedy search algo and the LinKernigan optimisation 🙂 This is part of the LK. I’ll give a look at advent of code and do them when i’ll have time, after finals are over ! 🙂

karelpeeters

12/13/2017, 3:06 PM

Ah that's funny, we had to reverse part of a list for one of the problems too.

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