From 608aa5d4cf207a1cae70f4dab2e1a8ba2d05c382 Mon Sep 17 00:00:00 2001
From: Nick Krichevsky <nick@ollien.com>
Date: Sat, 2 Dec 2023 08:47:29 -0500
Subject: [PATCH] Solve day 2

---
 day2/main.go | 186 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 186 insertions(+)
 create mode 100644 day2/main.go

diff --git a/day2/main.go b/day2/main.go
new file mode 100644
index 0000000..fd9c1af
--- /dev/null
+++ b/day2/main.go
@@ -0,0 +1,186 @@
+package main
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"regexp"
+	"strconv"
+	"strings"
+)
+
+type CubeCounts = map[string]int
+
+type Game struct {
+	id     int
+	rounds []CubeCounts
+}
+
+func main() {
+	if len(os.Args) != 2 {
+		fmt.Fprintf(os.Stderr, "Usage: %s inputfile\n", os.Args[0])
+		os.Exit(1)
+	}
+
+	filename := os.Args[1]
+	inputFile, err := os.Open(filename)
+	if err != nil {
+		panic(fmt.Sprintf("failed to open input file: %s", err))
+	}
+
+	inputBytes, err := io.ReadAll(inputFile)
+	if err != nil {
+		panic(fmt.Sprintf("failed to read input file: %s", err))
+	}
+
+	input := string(inputBytes)
+	inputLines := strings.Split(strings.TrimSpace(input), "\n")
+	games, err := parseGames(inputLines)
+	if err != nil {
+		panic(fmt.Sprintf("invalid input: %s", err))
+	}
+
+	fmt.Printf("Part 1: %d\n", part1(games))
+	fmt.Printf("Part 2: %d\n", part2(games))
+}
+
+func part1(games []Game) int {
+	invalidIDTotal := 0
+	for _, game := range games {
+		if isGameValid(game) {
+			invalidIDTotal += game.id
+		}
+	}
+
+	return invalidIDTotal
+}
+
+func part2(games []Game) int {
+	totalPower := 0
+	for _, game := range games {
+		minPossibleCubes := maxCubesByColor(game)
+		totalPower += cubePower(minPossibleCubes)
+	}
+
+	return totalPower
+}
+
+// isGameValid will check if the given game is valid by the number of cubes in the bag
+func isGameValid(game Game) bool {
+	cubeCounts := map[string]int{
+		"red":   12,
+		"green": 13,
+		"blue":  14,
+	}
+
+	for _, round := range game.rounds {
+		for color, count := range round {
+			if count > cubeCounts[color] {
+				return false
+			}
+		}
+	}
+
+	return true
+}
+
+// maxCubesByColor will get the maximum quantity of cubes for each color in the game's rounds
+func maxCubesByColor(game Game) CubeCounts {
+	maxCounts := CubeCounts{}
+	for _, round := range game.rounds {
+		for color, count := range round {
+			currentMax := maxCounts[color]
+			if count > currentMax {
+				maxCounts[color] = count
+			}
+		}
+	}
+
+	return maxCounts
+}
+
+// cubePower calculates the "power" of the cubes selected in a round
+func cubePower(cubes CubeCounts) int {
+	return cubes["red"] * cubes["green"] * cubes["blue"]
+}
+
+func parseGames(inputLines []string) ([]Game, error) {
+	return tryParse[Game](inputLines, parseGame)
+}
+
+func parseGame(line string) (Game, error) {
+	gameID, chosenCubes, err := splitGameLine(line)
+	if err != nil {
+		return Game{}, fmt.Errorf("invalid game %q: %w", line, err)
+	}
+
+	rounds, err := parseRounds(chosenCubes)
+	if err != nil {
+		return Game{}, fmt.Errorf("invalid rounds %q: %w", chosenCubes, err)
+	}
+
+	return Game{
+		id:     gameID,
+		rounds: rounds,
+	}, nil
+}
+
+func splitGameLine(line string) (int, string, error) {
+	gamesPattern := regexp.MustCompile(`^Game (\d+): (.*)$`)
+	matches := gamesPattern.FindStringSubmatch(line)
+	if matches == nil {
+		return 0, "", errors.New("malformed game line")
+	}
+
+	rawGameID := matches[1]
+	gameID, err := strconv.Atoi(rawGameID)
+	if err != nil {
+		// we already know this isn't going to happen from the regexp above
+		panic("game id was non-numeric")
+	}
+
+	return gameID, matches[2], nil
+}
+
+func parseRounds(roundsSpec string) ([]CubeCounts, error) {
+	roundSpecs := strings.Split(roundsSpec, ";")
+	return tryParse[CubeCounts](roundSpecs, parseRound)
+}
+
+func parseRound(round string) (CubeCounts, error) {
+	roundPattern := regexp.MustCompile(`(\d+) (\w+)`)
+	matches := roundPattern.FindAllStringSubmatch(round, -1)
+	if matches == nil {
+		return nil, errors.New("malformed round spec")
+	}
+
+	cubes := CubeCounts{}
+	for _, match := range matches {
+		color := match[2]
+		rawCubeCount := match[1]
+		count, err := strconv.Atoi(rawCubeCount)
+		if err != nil {
+			// we already know this isn't going to happen from the regexp above
+			panic("cube count was non-numeric")
+		}
+
+		cubes[color] = count
+	}
+
+	return cubes, nil
+}
+
+func tryParse[T any](items []string, parse func(string) (T, error)) ([]T, error) {
+	res := make([]T, 0, len(items))
+	for i, item := range items {
+		parsed, err := parse(item)
+		if err != nil {
+			return nil, fmt.Errorf("invalid item #%d: %w", i+1, err)
+		}
+
+		res = append(res, parsed)
+	}
+
+	return res, nil
+}