roger_federer.kt

package w34_roger_federer

data class Group(val token: String, val occurrences: Int)

private fun findGroupsAndCounts(input: String, size: Int): List<Group> {

    val groups = mutableListOf<Group>()

    for (i in 2..size) {

        val counts = input
            .windowed(i, 1) // Sliding window of size i
            .groupingBy { it } // Group by the token
            .eachCount() // And count the tokens

        groups.addAll(counts.map { Group(it.key, it.value) })
    }

    return groups
}

private fun findMostOccurringGroup(input: String): Group? {

    val groupsCounts = findGroupsAndCounts(input, input.length / 2)

    return groupsCounts.maxWithOrNull(
        compareBy<Group> { it.occurrences }
            .thenBy { it.token }
    )
}

private fun String.trimmed() = this
    .filter { it.isLetterOrDigit() }
    .lowercase()

fun main() {

    val string = "Roger Federer"

    val mostOccurring = findMostOccurringGroup(string.trimmed())

    if (mostOccurring != null && mostOccurring.occurrences > 1) {
        val percentage =
            (mostOccurring.occurrences.toDouble() * mostOccurring.token.length / string.trimmed().length * 100).toInt()
        println("$percentage% of $string is \"${mostOccurring.token}\"")
    } else {
        println("$string doesn't have any repeating groups.")
    }
}