Count Word and Find Rank

CountAndFindRankInWording.kts

fun Map<Int, List<Char>>.findRank(rank: Int): List<Char> {
    val e = this.entries.filterIndexed { index, entry ->
        index + 1 == rank
    }
    return e.map { it.value }.flatten()
}

fun countWord(input: String): Map<Int, List<Char>> {
    return input.groupBy { it }
        .mapValues { (_, values) -> values.size }
        .entries
        .sortedByDescending { it.value }
        .groupBy { it.value }
        .mapValues { (k, v) ->
            v.map {
                it.key
            }
        }
}

countWord("aabbcccddeeeeffffd")
    .findRank(2).forEach {
        println(it)
    }