Day 2: Gift Shop

My part 2 Kotlin solution:

val factors = intArrayOf(2, 3, 5, 7)

fun main() {
    var total = 0L
    val input = getInput(2)
    val ranges = parseInput1(input)
    ranges.forEach {
        val start = it.first.toLong()
        val end = it.second.toLong()
        for (id in start..end) {
            val idString = id.toString()
            if (isIdInvalid2(idString)) {
                total += id
            }
        }
    }
    println(total)
}

fun parseInput1(input: String): List<Pair<String, String>> {
    return input.split(",")
        .filter { it.isNotBlank() }
        .map {
            val secondSplit = it.split("-")
            secondSplit.first().trim() to secondSplit.last().trim()
        }
}

fun isIdInvalid2(id: String): Boolean {
    for (factor in factors) {
        if (id.length % factor == 0) {
            val gap = id.length / factor
            var areAllMatching = true
            for (i in 0..<gap) {
                val end = (factor - 1) * gap + i
                if (!areCharactersTheSame(id, gap, i, end)) {
                    areAllMatching = false
                    break
                }
            }
            if (areAllMatching) {
                return true
            }
        }
    }
    return false
}

fun areCharactersTheSame(string: String, gap: Int, start: Int, end: Int): Boolean {
    val character = string[start]
    for (i in start + gap..end step gap) {
        if (character != string[i]) {
            return false
        }
    }
    return true
}

I didn't look closely enough at the input to know how big an entire list of IDs would be huge or not. But I assumed it was. So instead I just did ranges as Pairs.

I also only considered the prime factors up to 7, because there weren't any IDs that needed any higher.

Edit: I also worried that a brute force solution might be slow, but being day 2, I might have been a little too worried about that. The main algorithm ran in 68ms.