Daily Coding Problem: Problem #541

/**
 * Good morning! Here's your coding interview problem for today.
This problem was asked by Amazon.
Run-length encoding is a fast and simple method of encoding strings. The basic idea is to represent repeated successive characters as a single count and character.
For example, the string "AAAABBBCCDAA" would be encoded as "4A3B2C1D2A".
Implement run-length encoding and decoding.
You can assume the string to be encoded have no digits and consists solely of alphabetic characters. You can assume the string to be decoded is valid.
 * */
class Problem_541 {
    
    fun decode(input: String): String {
        var numString = ""
        val sbOutput = StringBuilder()
        for (c in input) {
            if (c.isDigit()) {
                numString += c
            } else {
                val count = numString.toInt()
                for (i in 0 until count) {
                    sbOutput.append(c)
                }
                numString = ""
            }
        }
        return sbOutput.toString()
    }

    fun encode(input: String): String {
        val sbOutput = StringBuilder()
        var seen = ' '
        var count = 0
        for (c in input) {
            if (seen == c) {
                count++
            } else {
                //the first time we run this, will get an extra zero that we'll need to remove
                sbOutput.append(count).append(seen)
                seen = c
                //meet one char, so set the count to 1
                count = 1
            }
        }
        val result = sbOutput.deleteCharAt(0).trim().toString()
        return result
    }
}