lastIndexOF

  private fun String.lastIndexOf(char: Char): Int {
        var bOpen = 0     // count for open bracket
        var bClose = 0    // count for close bracket
        for (i in this.indices) {
            val currChar = this[i]

            when {
                currChar == char && bOpen == bClose -> 
                                    return this.length - i - 1
                currChar == '(' -> bOpen++
                currChar == ')' -> bClose++
            }
        }
        return -1
    }