gazolla / kotlin-algorithm

Algorithms and data structures in kotlin

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kotlin-algorithm's Issues

Contribute to my fork, I'm seeking your help to keep it up-to-date

This project hasn't been updated for quite some time. I invite you to contribute to my fork, and I'm seeking your assistance in keeping it up-to-date.

https://github.com/Amir-yazdanmanesh/Kotlin-Algorithm

Improvement suggestions for shuffle

I was looking for code to do shuffle. I feel there are two problems with your solution:

1. the function mutates the list given to it (and sort of pretends that it didn't by returning the result of the shuffle additionally as it's return value)
2. it doesn't use existing code for shuffling

I wrote this code for my project:

/**
 * Returns a randomized list.
 */
fun <T> Iterable<T>.shuffle(seed: Long? = null): List<T> {
    val list = this.toMutableList()
    val random = if (seed != null) Random(seed) else Random()
    Collections.shuffle(list, random)
    return list
}

It reuses existing code to do the shuffling and can be called like other kotlin collection functions.

Shuffle isn't correct

fun <T:Comparable<T>>shuffle(items:MutableList<T>):List<T>{
    val rg : Random = Random()
    for (i in 0..items.size - 1) {
        val randomPosition = rg.nextInt(items.size)
        val tmp : T = items[i]
        items[i] = items[randomPosition]
        items[randomPosition] = tmp
    }
    return items
}

This algorithm doesn't shuffle it correctly, not every permutation is equiprobable. You have to do:

val randomPosition = rg.nextInt(i + 1)

to fix it.

More information:
https://blog.codinghorror.com/the-danger-of-naivete/

various clarifications for inclusion as external libs

I just googled for a Kotlin Stack class and found this library...

i'd like to open this up for discussion:

things that are currently undefined:

no POM -- was there ever any intent or success with:
git submodule add https://github.com/<User>/Kotlin-Algorithm.git
?

no packages declared in the kotlin source -- curious things happen with root package in jvm

no README declaration of whether this lib attempts pure java or js stdlib -- inconsistent due to:

junit imports in the same hierarchy as the source code -- tests are nice... but this lib is inconsistent.

i'd like to use the simple Stack class and go back to playing with my own project... but my inclination is to suggest one of the active maintainers provide one or more or pom, gradle, and raw git submodule imports, with package hierarchy chosen ... git submodule add "Kotlin-Algorithm" into src/main/kotlin does not imply a pleasant packagename, but there's no reason it could not be robust as a git submodule.

for now i'm fine cutting and pasting these gems, but had to scratch my head a minute to figure out what is going on, an unexpected cost.

merge sort dosen't work correctly

the merge sort result is always null or empty