String Compressor

class Compressor {

    fun compress(s: String): String {
        val b = StringBuilder()
        var cnt = 0
        var rChar: Char = s[0]
        for(ch in s) {
            if(cnt == 0) {
                rChar = ch
            }

            if(ch == rChar) {
                cnt++
            } else {
                b.appendRepeat(cnt, rChar)

                cnt = 1
                rChar = ch
            }
        }

        if(cnt == 1) {
            b.append(rChar)
        } else {
            b.appendRepeat(cnt, rChar)
        }

        return b.toString()
    }

    private fun StringBuilder.appendRepeat(repeatCnt: Int, ch: Char) {
        append(repeatCnt.toString())
        append(ch)
    }

}