From 1fd91cb3430141ee2968868f01dc9674de80a611 Mon Sep 17 00:00:00 2001
From: Anna Wiggins <annabunches@gmail.com>
Date: Fri, 11 Dec 2020 04:22:00 +0000
Subject: [PATCH] Add day 7 solution.

---
 2020/day07.go | 113 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 113 insertions(+)
 create mode 100644 2020/day07.go

diff --git a/2020/day07.go b/2020/day07.go
new file mode 100644
index 0000000..d07702a
--- /dev/null
+++ b/2020/day07.go
@@ -0,0 +1,113 @@
+package main
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"regexp"
+	"strconv"
+
+	"git.annabunch.es/annabunches/adventofcode/2020/lib/fileutils"
+)
+
+type Node struct {
+	Color    string
+	Children map[*Node]int
+}
+
+var nodeMap map[string]*Node
+
+var colorRe = regexp.MustCompile("^(.*?) bags contain")
+var childRe = regexp.MustCompile("(?:contain|,) (\\d+) (.*?) bag")
+
+func findOrCreateNode(color string) *Node {
+	if node, ok := nodeMap[color]; ok {
+		return node
+	}
+
+	node := &Node{
+		Color: color,
+	}
+	nodeMap[color] = node
+	return node
+}
+
+func parseRule(line string) {
+	if line == "" {
+		return
+	}
+
+	color := colorRe.FindStringSubmatch(line)[1]
+
+	node := findOrCreateNode(color)
+
+	children := make(map[*Node]int)
+	childrenData := childRe.FindAllStringSubmatch(line, 128)
+
+	for _, childData := range childrenData {
+		child := findOrCreateNode(childData[2])
+		count, err := strconv.Atoi(childData[1])
+		if err != nil {
+			log.Panicf(err.Error())
+		}
+		children[child] = count
+	}
+
+	node.Children = children
+}
+
+func findInDescendants(node *Node, color string) bool {
+	for child, _ := range node.Children {
+		if rFindInDescendants(child, color) {
+			return true
+		}
+	}
+	return false
+}
+
+func rFindInDescendants(node *Node, color string) bool {
+	// found it
+	if node.Color == color {
+		return true
+	}
+
+	for child, _ := range node.Children {
+		if rFindInDescendants(child, color) {
+			return true
+		}
+	}
+	return false
+}
+
+func countChildren(node *Node) int {
+	total := 1 // count ourself
+	for child, count := range node.Children {
+		total += count * countChildren(child)
+	}
+	return total
+}
+
+func main() {
+	step := os.Args[1]
+	values := fileutils.InputParserStrings(os.Args[2])
+
+	nodeMap = make(map[string]*Node)
+
+	for _, line := range values {
+		parseRule(line)
+	}
+
+	switch step {
+	case "1":
+		total := 0
+		for _, node := range nodeMap {
+			if findInDescendants(node, "shiny gold") {
+				total++
+			}
+		}
+		fmt.Println("Total:", total)
+
+	case "2":
+		fmt.Println("Total:", countChildren(nodeMap["shiny gold"])-1)
+	}
+}