Add day 6 part 1

day6/main.go

@@ -0,0 +1,138 @@
+package main
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"regexp"
+	"strconv"
+	"strings"
+)
+
+type Race struct {
+	time           int
+	recordDistance int
+}
+
+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")
+	races, err := parseRaces(inputLines)
+	if err != nil {
+		panic(fmt.Sprintf("failed to parse races: %s", err))
+	}
+
+	fmt.Printf("Part 1: %d\n", part1(races))
+	// fmt.Printf("Part 2: %d\n", part2(seeds, conversions, workSize))
+}
+
+func part1(races []Race) int {
+	res := 1
+	for _, race := range races {
+		possibleWins := 0
+		for timeHeld := 0; timeHeld <= race.time; timeHeld++ {
+			distance := distanceForTimeHeld(timeHeld, race.time)
+			if distance > race.recordDistance {
+				possibleWins++
+			}
+		}
+
+		res *= possibleWins
+	}
+
+	return res
+}
+
+func distanceForTimeHeld(buttonHeld int, raceTime int) int {
+	timeLeft := raceTime - buttonHeld
+	speed := buttonHeld
+
+	return speed * timeLeft
+}
+
+func parseRaces(lines []string) ([]Race, error) {
+	if len(lines) != 2 {
+		return nil, errors.New("input must be exactly two lines")
+	}
+
+	timeLine := removeRowPrefix(lines[0], "Time")
+	distanceLine := removeRowPrefix(lines[1], "Distance")
+
+	if timeLine == lines[0] {
+		return nil, errors.New("malformed 'time' line")
+	} else if distanceLine == lines[1] {
+		return nil, errors.New("malformed 'distance' line")
+	}
+
+	spacePattern := regexp.MustCompile(`\s+`)
+	rawTimeLineComponents := spacePattern.Split(timeLine, -1)
+	rawDistanceLineComponents := spacePattern.Split(distanceLine, -1)
+	if len(rawTimeLineComponents) != len(rawDistanceLineComponents) {
+		return nil, errors.New("'time' and 'distance' lines have a different number of elements")
+	}
+
+	timeLineComponents, err := tryParse(rawTimeLineComponents, strconv.Atoi)
+	if err != nil {
+		return nil, fmt.Errorf("invalid element in 'time' line: %w", err)
+	}
+
+	distanceLineComponents, err := tryParse(rawDistanceLineComponents, strconv.Atoi)
+	if err != nil {
+		return nil, fmt.Errorf("invalid element in 'distance' line: %w", err)
+	}
+
+	races := make([]Race, len(timeLineComponents))
+	for i := 0; i < len(timeLineComponents); i++ {
+		timeComponent := timeLineComponents[i]
+		distanceComponent := distanceLineComponents[i]
+		races[i] = Race{
+			time:           timeComponent,
+			recordDistance: distanceComponent,
+		}
+	}
+
+	return races, nil
+}
+
+func removeRowPrefix(s string, prefix string) string {
+	pattern := regexp.MustCompile("^" + regexp.QuoteMeta(prefix) + `:\s*`)
+
+	return pattern.ReplaceAllLiteralString(s, "")
+}
+
+func tryParse[T any](items []string, doParse func(s string) (T, error)) ([]T, error) {
+	res := []T{}
+	for i, line := range items {
+		parsedItem, err := doParse(line)
+		if err != nil {
+			return nil, fmt.Errorf("malformed item at index %d: %w", i, err)
+		}
+
+		res = append(res, parsedItem)
+	}
+
+	return res, nil
+}