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class Day08(rawInput: String) {
    private val tree: Node = Node.of(rawInput.split(" ").map { it.toInt() }.iterator())

    fun solvePart1(): Int =
        tree.metadataTotal

    fun solvePart2(): Int =
        tree.value

    private class Node(children: List<Node>, metadata: List<Int>) {
        companion object {
            fun of(values: Iterator<Int>): Node {
                val numChildren: Int = values.next()
                val numMetadata: Int = values.next()
                val children = (0 until numChildren).map { Node.of(values) }
                val metadata = (0 until numMetadata).map { values.next() }.toList()
                return Node(children, metadata)
            }
        }

        val metadataTotal: Int =
            metadata.sum() + children.sumBy { it.metadataTotal }

        val value: Int =
            if (children.isEmpty()) metadata.sum()
            else metadata.map { children.getSafely(it)?.value ?: 0 }.sum()

        private fun List<Node>.getSafely(i: Int): Node? =
            if (i > this.size) null
            else this[i - 1]

    }
}

tailrec

List(...) { ... }

callatz_tailrec

n

911/563 ms

7972/5725 ms

Process finished with exit code -1,073,741,571.

LinkedList

listIterator()

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