day 12

12/input.txt

@@ -0,0 +1,26 @@
+start-YY
+av-rz
+rz-VH
+fh-av
+end-fh
+sk-gp
+ae-av
+YY-gp
+end-VH
+CF-qz
+qz-end
+qz-VG
+start-gp
+VG-sk
+rz-YY
+VH-sk
+rz-gp
+VH-av
+VH-fh
+sk-rz
+YY-sk
+av-gp
+rz-qz
+VG-start
+sk-fh
+VG-av

12/main.go

@@ -0,0 +1,94 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"log"
+	"os"
+	"strings"
+)
+
+type Graph struct {
+	nodes map[string]*Node
+}
+
+type Node struct {
+	name       string
+	neighbours []string
+}
+
+func (g *Graph) addNode(location string) {
+	if _, ok := g.nodes[location]; !ok {
+		g.nodes[location] = &Node{location, make([]string, 0)}
+	}
+}
+
+func (g *Graph) addNeighbour(location, neighbourLocation string) {
+	node := g.nodes[location]
+	node.neighbours = append(node.neighbours, neighbourLocation)
+	node = g.nodes[neighbourLocation]
+	node.neighbours = append(node.neighbours, location)
+}
+
+func (g *Graph) walk(n *Node, visited []string, target string, revisited bool) bool {
+	if strings.ToLower(n.name) == n.name {
+		for _, v := range visited {
+			if v == n.name {
+				if revisited || !partTwo {
+					return false
+				} else {
+					revisited = true
+				}
+			}
+		}
+	}
+	visited = append(visited, n.name)
+
+	if n.name == target {
+		total++
+		return true
+	}
+	for _, neighbourLocation := range n.neighbours {
+		if neighbourLocation == "start" {
+			continue
+		}
+		node, ok := g.nodes[neighbourLocation]
+		if !ok {
+			return false
+		}
+		g.walk(node, visited, target, revisited)
+	}
+	return false
+}
+
+var total int
+var partTwo bool
+
+func main() {
+	file, err := os.Open("input.txt")
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer file.Close()
+
+	scanner := bufio.NewScanner(file)
+	scanner.Split(bufio.ScanLines)
+
+	graph := Graph{make(map[string]*Node)}
+
+	for scanner.Scan() {
+		line := scanner.Text()
+		path := strings.Split(line, "-")
+		graph.addNode(path[0])
+		graph.addNode(path[1])
+		graph.addNeighbour(path[0], path[1])
+	}
+
+	start := graph.nodes["start"]
+	visited := []string{}
+	graph.walk(start, visited, "end", false)
+	fmt.Println(total)
+	partTwo, total = true, 0
+	graph.walk(start, visited, "end", false)
+	fmt.Println(total)
+}