Add solution for day 8.

day8.cr

@@ -0,0 +1,49 @@
+require "./common.cr"
+
+lines = File.read("day8_input").split("\n")
+lines.pop
+
+class Node
+  getter children : Array(Node)
+  getter metadata : Array(Int32)
+
+  def initialize(@children : Array(Node), @metadata : Array(Int32))
+  end
+
+  def sum
+    return metadata.sum + children.map(&.sum.as Int32).sum
+  end
+
+  def value
+    return metadata.sum if children.empty?
+    metadata.map do |meta|
+      next 0 unless child = children[meta - 1]?
+      next child.value
+    end.sum
+  end
+end
+
+def parse(numbers, index = 0)
+  child_count = numbers[index]
+  index += 1
+  meta_count = numbers[index]
+  index += 1
+
+
+  children = Array(Node).new
+  child_count.times do |count|
+    child, index = parse(numbers, index)
+    children << child
+  end
+
+  meta = numbers[index...(index + meta_count)]
+  index += meta_count
+  
+  node = Node.new children, meta
+  return {node, index}
+end
+
+numbers = lines[0].split(" ").map &.to_i32
+tree = parse(numbers)
+puts tree[0].sum
+puts tree[0].value