AOC - 2024 day 7

package Y2024.D7

class Calculations(lines: List<String>) {
    val calculations = mutableMapOf<Long, List<Long>>()

    init {
        lines.map { it.split(" ") }.map {
            val sum = it[0].replace(":", "").toLong()
            calculations[sum] = it.subList(1, it.size).map { it.toLong() }
        }
    }

    fun sumOfTrueSums(): Long {
        return calculations.entries.filter {
            checkSum(it.key, it.value[0], it.value.subList(1, it.value.size))
        }.sumOf { it.key }
    }

    private fun checkSum(sum: Long, running: Long, numbers: List<Long>): Boolean {
        if (sum < running) return false
        if (numbers.isEmpty()) return sum == running
        return checkSum(sum, running * numbers[0], numbers.subList(1, numbers.size))
                || checkSum(sum, running + numbers[0], numbers.subList(1, numbers.size))
    }

    fun sumOfTrueSumsThreeOps(): Long {
        return calculations.entries.filter {
            checkSumThreeOps(it.key, it.value[0], it.value.subList(1, it.value.size))
        }.sumOf { it.key }
    }

    private fun checkSumThreeOps(sum: Long, running: Long, numbers: List<Long>): Boolean {
        if (sum < running) return false
        if (numbers.isEmpty()) return sum == running
        return checkSumThreeOps(sum, running * numbers[0], numbers.subList(1, numbers.size))
                || checkSumThreeOps(sum, running + numbers[0], numbers.subList(1, numbers.size))
                || checkSumThreeOps(sum,  "${running}${numbers[0]}".toLong(), numbers.subList(1, numbers.size))
    }
}