From 18b911204ef9d939269bdc227a1fcd642f821a6b Mon Sep 17 00:00:00 2001
From: Nick Krichevsky <nick@ollien.com>
Date: Fri, 8 Dec 2023 17:28:25 -0500
Subject: [PATCH] Add day 8 part 1

---
 day8/main.go | 143 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 143 insertions(+)
 create mode 100644 day8/main.go

diff --git a/day8/main.go b/day8/main.go
new file mode 100644
index 0000000..5485a91
--- /dev/null
+++ b/day8/main.go
@@ -0,0 +1,143 @@
+package main
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"regexp"
+	"strings"
+)
+
+type Direction int
+type NodeAddress string
+
+const (
+	DirectionLeft Direction = iota
+	DirectionRight
+)
+
+const (
+	NodeAddressStart NodeAddress = "AAA"
+	NodeAddressEnd   NodeAddress = "ZZZ"
+)
+
+type NodeChoice struct {
+	left  NodeAddress
+	right NodeAddress
+}
+
+// TakeDirection will take the node in the given direction. Panics if an invalid direction is given
+func (choice NodeChoice) TakeDirection(direction Direction) NodeAddress {
+	switch direction {
+	case DirectionLeft:
+		return choice.left
+	case DirectionRight:
+		return choice.right
+	default:
+		panic("invalid direction value")
+	}
+}
+
+func main() {
+	if len(os.Args) != 2 && len(os.Args) != 3 {
+		fmt.Fprintf(os.Stderr, "Usage: %s inputfile\n", os.Args[0])
+		os.Exit(1)
+	}
+
+	inputFilename := os.Args[1]
+	inputFile, err := os.Open(inputFilename)
+	if err != nil {
+		panic(fmt.Sprintf("could not open input file: %s", err))
+	}
+
+	defer inputFile.Close()
+
+	inputBytes, err := io.ReadAll(inputFile)
+	if err != nil {
+		panic(fmt.Sprintf("could not read input file: %s", err))
+	}
+
+	input := strings.TrimSpace(string(inputBytes))
+	if err != nil {
+		panic(fmt.Sprintf("failed to parse input: %s", err))
+	}
+
+	inputLines := strings.Split(input, "\n")
+	if len(inputLines) < 3 {
+		panic("not enough data in input to parse")
+	}
+
+	directions, err := parseDirectionLine(inputLines[0])
+	if err != nil {
+		panic(fmt.Sprintf("failed to parse direction lien: %s", err))
+	}
+
+	nodeMap, err := parseMap(inputLines[2:])
+	if err != nil {
+		panic(fmt.Sprintf("failed to parse map: %s", err))
+	}
+
+	fmt.Printf("Part 1: %d\n", part1(directions, nodeMap))
+}
+
+func part1(directions []Direction, nodeMap map[NodeAddress]NodeChoice) int {
+	directionCursor := 0
+	currentNode := NodeAddressStart
+	steps := 0
+
+	for currentNode != NodeAddressEnd {
+		if currentNode == NodeAddressEnd {
+			return steps
+		}
+
+		direction := directions[directionCursor]
+		currentNode = nodeMap[currentNode].TakeDirection(direction)
+		directionCursor = (directionCursor + 1) % len(directions)
+		steps++
+	}
+
+	return steps
+}
+
+func parseDirectionLine(line string) ([]Direction, error) {
+	directions := make([]Direction, len(line))
+	for i, char := range line {
+		if char == 'L' {
+			directions[i] = DirectionLeft
+		} else if char == 'R' {
+			directions[i] = DirectionRight
+		} else {
+			return nil, fmt.Errorf("invalid direction char '%c'", char)
+		}
+	}
+
+	return directions, nil
+}
+
+func parseMap(lines []string) (map[NodeAddress]NodeChoice, error) {
+	mapNodes := make(map[NodeAddress]NodeChoice, len(lines))
+	for _, line := range lines {
+		source, choice, err := parseMapLine(line)
+		if err != nil {
+			return nil, fmt.Errorf("could not parse %q: %w", line, err)
+		}
+
+		mapNodes[source] = choice
+	}
+
+	return mapNodes, nil
+}
+
+func parseMapLine(line string) (NodeAddress, NodeChoice, error) {
+	pattern := regexp.MustCompile(`^([A-Z]{3}) = \(([A-Z]{3}), ([A-Z]{3})\)$`)
+	matches := pattern.FindStringSubmatch(line)
+	if matches == nil {
+		return "", NodeChoice{}, errors.New("malformed line")
+	}
+
+	source := NodeAddress(matches[1])
+	choice := NodeChoice{left: NodeAddress(matches[2]), right: NodeAddress(matches[3])}
+
+	return source, choice, nil
+}