Day 8

src/main/kotlin/com/basdado/adventofcode/Day8.kt

@@ -0,0 +1,77 @@
+package com.basdado.adventofcode
+
+import java.util.stream.Stream
+
+fun main() {
+    val day = Day8()
+    day.puzzle1()
+    day.puzzle2()
+}
+
+class Day8 {
+
+    fun puzzle1() {
+        val root = parseInput()
+        println(flatMap(root) { it.metadata.stream() }.mapToInt{ it }.sum())
+    }
+
+    fun puzzle2() {
+        val root = parseInput()
+        println(findValue(root))
+    }
+
+    private fun parseInput(): Node {
+        val input = lines("/day/8/input.txt")
+            .findFirst().get()
+            .split(Regex("""\s+"""))
+            .map { it.toInt() }
+            .toIntArray()
+
+        return parse(input)
+    }
+
+    fun parse(arr: IntArray, startIndex: Int = 0): Node {
+
+        var index = startIndex;
+        val nodeCount = arr[index++]
+        val metadataCount = arr[index++]
+
+        var children = mutableListOf<Node>()
+        for (i in 0 until nodeCount) {
+            val newChild = parse(arr, index)
+            index = newChild.endIndex
+            children.add(newChild)
+        }
+        val metadata = arr.copyOfRange(index, index + metadataCount).toList()
+        index += metadataCount
+
+        return Node(children, metadata, index)
+    }
+
+    fun <T> flatMap(node: Node, mapping: Function1<Node, Stream<T>>): Stream<T> {
+
+        var res = mapping.invoke(node)
+        for (child in node.children) {
+            res = Stream.concat(res, flatMap(child, mapping))
+        }
+        return res
+    }
+
+    fun findValue(node: Node): Int {
+
+        if (node.children.isEmpty()) {
+            return node.metadata.toIntArray().sum()
+        } else {
+            var sum = 0
+            for (index in node.metadata) {
+
+                if (index > 0 && index <= node.children.size) {
+                    sum += findValue(node.children[index - 1])
+                }
+            }
+            return sum
+        }
+    }
+
+    data class Node (val children: List<Node>, val metadata: List<Int>, val endIndex: Int)
+}