nthfrequent2.kt

fun firstIndexOfNthMostFrequentChar(str: String, n: Int): Int {
    val countsMap = createCountsMap(str)
    if (countsMap.size < n) {
        return -1
    }
    
    val sortedKeyValuePairs = sortKeyValuePairs(countsMap)
   
    val ch = sortedKeyValuePairs[n-1].first
    return str.indexOf(ch, 0)
}

fun sortKeyValuePairs(map: Map<Char, Int>): List<Pair<Char, Int>> {
    val pairs: MutableList<Pair<Char, Int>> =  map.toList().toMutableList()
    pairs.sortBy{ -it.second  }
    return pairs
}

fun createCountsMap(str: String): Map<Char, Int> {
    val result: MutableMap<Char, Int> = mutableMapOf()
    for (ch in str) {
        var count = result.getOrPut(ch, {0})
        result.put(ch, ++count)
    }
    return result
}