Really simple somewhat functional filter for getting rid of duplicates in ROM sets

filter.kt

import java.io.File

fun main(args: Array<String>) {
    val files = File("/path/to/roms/Game Boy").listFiles()
    files.sortBy { it.name }

    val gameNames = mutableListOf<String>()

    for (file in files) {
        val gameName = file.name.substringBefore(" (")
        
        if (!gameNames.contains(gameName)) {
            gameNames.add(gameName)
        }
    }

    val okRoms = mutableListOf<File>()

    for (name in gameNames) {
        val romsForName = mutableListOf<File>()

        for (file in files) {
            val gameName = file.name.substringBefore(" (")
            if (name == gameName) {
                romsForName.add(file)
            }
        }

        if (romsForName.count() == 1) {
            okRoms.add(romsForName[0])
            continue
        }

        val noBrackets = romsForName.filter { !it.name.contains("[")}
        if (noBrackets.count() > 0) {
            okRoms.addAll(noBrackets)
            continue
        }

        val exclamationPoint = romsForName.filter { it.name.contains("[!]") }
        if (exclamationPoint.count() > 0) {
            okRoms.addAll(exclamationPoint)
            continue
        }

        okRoms.add(romsForName[0])
    }

    okRoms.sortBy { it.name }

    for (file in files) {
        if (!okRoms.contains(file)) {
            file.delete()
        }
    }
}