Day 8.2 solution.

2018/day08-1.go

@@ -14,10 +14,7 @@ func main() {
 }
 
 func sumMetadata(node *day08.Node) int {
-	sum := 0
+	sum := node.SumMetadata()
-	for _, v := range node.Metadata {
-		sum += v
-	}
 
 	for _, child := range node.Children {
 		sum += sumMetadata(child)

2018/day08-2.go

@@ -0,0 +1,36 @@
+package main
+
+import (
+	"fmt"
+
+	"internal/day08"
+	"internal/util"
+)
+
+func main() {
+	data := util.ReadInputInts()
+	root := day08.BuildTree(data)
+	fmt.Println(generateChecksum(root))
+}
+
+func generateChecksum(node *day08.Node) int {
+	// If a node has no child nodes, its value is the sum of its metadata entries.
+	if len(node.Children) == 0 {
+		return node.SumMetadata()
+	}
+
+	// if a node does have child nodes, the metadata entries become (1-indexed) indexes
+	// which refer to those child nodes.
+	// The value of the node is the sum of the values of its children.
+	value := 0
+	for _, md := range node.Metadata {
+		// Skip invalid metadata entries
+		if md == 0 || md > len(node.Children) {
+			continue
+		}
+
+		value += generateChecksum(node.Children[md-1])
+	}
+
+	return value
+}

2018/internal/day08/tree.go

@@ -5,6 +5,14 @@ type Node struct {
 	Metadata []int
 }
 
+func (node Node) SumMetadata() int {
+	sum := 0
+	for _, v := range node.Metadata {
+		sum += v
+	}
+	return sum
+}
+
 func BuildTree(data []int) *Node {
 	root, _ := buildTreeR(data, 0)
 	return root