https://stackoverflow.com/questions/59275176/how-to-optimize-this-algorithm-which-focus-on-finding-shortest-balanced-substrin

find_shortest_balanced_substring.kt

fun main() {
    println(solution("azABaabza"))
    println(solution("ABcabbCa"))
    println(solution("azABaabza"))
    println(solution("CATattac"))
    println(solution("TacoCat"))
    println(solution("Madam"))
    println(solution("AcZCbaBz"))
    println(solution("aZABcabbCa"))
}

fun solution(S: String): Int {
    for (k in 1..S.length) {
        for (i in 0 until S.length - k + 1) {
            val lowerSet = mutableSetOf<Char>()
            val upperSet = mutableSetOf<Char>()
            val temp = S.substring(i, i + k)
            for (ch in temp) {
                if (ch.isLowerCase()) lowerSet.add(ch) else upperSet.add(ch)
            }

            if (containsAllElements(lowerSet, upperSet) && containsAllElements(upperSet, lowerSet)) {
                return temp.length
            }
        }
    }
    return -1
}

fun containsAllElements(first: Set<Char>, second: Set<Char>): Boolean {
    val firstLower = first.map { it.toLowerCase() }
    val secondLower = second.map { it.toLowerCase() }

    return firstLower.containsAll(secondLower)
}