BinString.Procedural.kt

// Write a function parseBinaryInt() that accepts a string of binary digits and converts the value
// to its integer representation.

fun parseBinaryInt(num: String): Int {
  if (!valid(num)) {
    throw RuntimeException("error")
  } 
  
  var sum = 0
  var offset = 0
  val length = num.length - 1
  
  
  // 2^(length-offset) * Int.parse(char)
  for (char in num) {
    val zeroOrOne: Int = char.toString().toInt()
    sum += zeroOrOne * pow(2, length - offset)
    offset += 1
  }
  
  return sum
}

fun binStringToInt(binString: String): Int {
  val length = binString.length - 1
  if (valid(num)) { 
    return binString.toCharArray()
    .map({it.toString().toInt()})
    .reduceIndexed({index, acc, digit ->
        return acc + digit * 2f.pow(length - index)
    })
  } else {
    throw RuntimeException("Invalid string. Must be non-empty binary string".)
  }
}

private fun pow(base: Int, exponent: Int): Int {
  var total = 1
  for (i in 1..exponent) {
    total *= base
  }
  return total
}


private fun valid(str: String): Boolean {
  return str.length > 0 && "[0-1]*".toRegex().matches(str)
}

fun main(args: Array<String>) {
  println(binStringToInt("111"))      // 7
  println(binStringToInt("10000"))    // 16
  println(binStringToInt("1000110"))  // 70
  println(binStringToInt("11111111"))  // 255
  try {
    println(binStringToInt("11BBCCC"))  // error
  } catch (e: Exception) {
    println(e)
  }
}