feat: solve part two using exhaustive search

internal/2015/DayFourteen/code.go

@@ -0,0 +1,108 @@
+package dayfourteen
+
+import (
+	"advent-of-code/internal/registry"
+	"os"
+	"regexp"
+	"strconv"
+	"strings"
+)
+
+var reindeerPattern = regexp.MustCompile(`\w+ can fly (\d+) km/s for (\d+) seconds, but then must rest for (\d+) seconds\.`)
+
+const raceTime = 2503
+
+type Reindeer struct {
+	Speed    int
+	FlyTime  int
+	RestTime int
+	Points   int
+}
+
+func init() {
+	registry.Register("2015D14", ParseInput, PartOne, PartTwo)
+}
+
+func ParseInput(filepath string) []string {
+	content, _ := os.ReadFile(filepath)
+	return strings.Split(string(content), "\n")
+}
+
+func parseReindeer(line string) Reindeer {
+	matches := reindeerPattern.FindStringSubmatch(line)
+	speed, _ := strconv.Atoi(matches[1])
+	flyTime, _ := strconv.Atoi(matches[2])
+	restTime, _ := strconv.Atoi(matches[3])
+	return Reindeer{Speed: speed, FlyTime: flyTime, RestTime: restTime}
+}
+
+func parseReindeers(data []string) []Reindeer {
+	reindeers := make([]Reindeer, 0, len(data))
+	for _, line := range data {
+		reindeers = append(reindeers, parseReindeer(line))
+	}
+	return reindeers
+}
+
+func (reindeer Reindeer) distanceAtTime(time int) int {
+	cycleTime := reindeer.FlyTime + reindeer.RestTime
+	fullCycles := time / cycleTime
+	distance := fullCycles * reindeer.Speed * reindeer.FlyTime
+	remainingTime := time % cycleTime
+	distance += reindeer.Speed * min(remainingTime, reindeer.FlyTime)
+	return distance
+}
+
+func calculateMaxDistance(data []string, time int) int {
+	reindeers := parseReindeers(data)
+	maxDistance := 0
+
+	for _, reindeer := range reindeers {
+		distance := reindeer.distanceAtTime(time)
+		if distance > maxDistance {
+			maxDistance = distance
+		}
+	}
+
+	return maxDistance
+}
+
+func calculateMaxPoints(data []string, time int) int {
+	reindeers := parseReindeers(data)
+
+	for second := 1; second <= time; second++ {
+		maxDistance := 0
+		distances := make([]int, len(reindeers))
+
+		for idx := range reindeers {
+			distance := reindeers[idx].distanceAtTime(second)
+			distances[idx] = distance
+			if distance > maxDistance {
+				maxDistance = distance
+			}
+		}
+
+		for idx := range reindeers {
+			if distances[idx] == maxDistance {
+				reindeers[idx].Points++
+			}
+		}
+	}
+
+	maxPoints := 0
+	for idx := range reindeers {
+		if reindeers[idx].Points > maxPoints {
+			maxPoints = reindeers[idx].Points
+		}
+	}
+
+	return maxPoints
+}
+
+func PartOne(data []string) int {
+	return calculateMaxDistance(data, raceTime)
+}
+
+func PartTwo(data []string) int {
+	return calculateMaxPoints(data, raceTime)
+}

internal/2015/DayFourteen/code_test.go

@@ -0,0 +1,24 @@
+package dayfourteen
+
+import "testing"
+
+var testInput = []string{
+	"Comet can fly 14 km/s for 10 seconds, but then must rest for 127 seconds.",
+	"Dancer can fly 16 km/s for 11 seconds, but then must rest for 162 seconds.",
+}
+
+func TestPartOne(t *testing.T) {
+	expected := 1120
+	got := calculateMaxDistance(testInput, 1000)
+	if got != expected {
+		t.Errorf("calculateMaxDistance(testInput, 1000) = %d, want %d", got, expected)
+	}
+}
+
+func TestPartTwo(t *testing.T) {
+	expected := 689
+	got := calculateMaxPoints(testInput, 1000)
+	if got != expected {
+		t.Errorf("calculateMaxPoints(testInput, 1000) = %d, want %d", got, expected)
+	}
+}

internal/2015/register.go

@@ -5,6 +5,7 @@ import (
 	_ "advent-of-code/internal/2015/DayEleven"
 	_ "advent-of-code/internal/2015/DayFive"
 	_ "advent-of-code/internal/2015/DayFour"
+	_ "advent-of-code/internal/2015/DayFourteen"
 	_ "advent-of-code/internal/2015/DayNine"
 	_ "advent-of-code/internal/2015/DayOne"
 	_ "advent-of-code/internal/2015/DaySeven"

internal/2016/DayFive/code.go

@@ -19,15 +19,16 @@ func ParseInput(filepath string) string {
 
 func PartOne(data string) int {
 	doorIDBytes := []byte(data)
+	doorIDLen := len(doorIDBytes)
+	input := make([]byte, doorIDLen, doorIDLen+20)
+	copy(input, doorIDBytes)
 	password := make([]byte, 0, 8)
 	index := 0
 	hexChars := "0123456789abcdef"
-	var buffer []byte
 
 	for len(password) < 8 {
-		buffer = strconv.AppendInt(buffer[:0], int64(index), 10)
+		indexBytes := strconv.AppendInt(input[:doorIDLen], int64(index), 10)
-		input := append(doorIDBytes, buffer...)
+		hash := md5.Sum(indexBytes)
-		hash := md5.Sum(input)
 
 		if hash[0] == 0 && hash[1] == 0 && hash[2] < 16 {
 			char := hexChars[hash[2]&0x0F]
@@ -41,5 +42,32 @@ func PartOne(data string) int {
 }
 
 func PartTwo(data string) int {
+	doorIDBytes := []byte(data)
+	doorIDLen := len(doorIDBytes)
+	input := make([]byte, doorIDLen, doorIDLen+20)
+	copy(input, doorIDBytes)
+	password := make([]byte, 8)
+	filled := make([]bool, 8)
+	filledCount := 0
+	index := 0
+	hexChars := "0123456789abcdef"
+
+	for filledCount < 8 {
+		indexBytes := strconv.AppendInt(input[:doorIDLen], int64(index), 10)
+		hash := md5.Sum(indexBytes)
+
+		if hash[0] == 0 && hash[1] == 0 && hash[2] < 16 {
+			position := int(hash[2] & 0x0F)
+			if position < 8 && !filled[position] {
+				char := hexChars[hash[3]>>4]
+				password[position] = char
+				filled[position] = true
+				filledCount++
+			}
+		}
+		index++
+	}
+
+	fmt.Println(string(password))
 	return 0
 }

internal/2016/DayFive/code_test.go

@@ -32,3 +32,27 @@ func TestPartOne(t *testing.T) {
 		t.Errorf("PartOne() printed %q, want %q", got, expected)
 	}
 }
+
+func TestPartTwo(t *testing.T) {
+	expected := "05ace8e3"
+
+	oldStdout := os.Stdout
+	r, w, err := os.Pipe()
+	if err != nil {
+		t.Fatalf("Failed to create pipe: %v", err)
+	}
+	os.Stdout = w
+
+	PartTwo(testInput)
+
+	_ = w.Close()
+	os.Stdout = oldStdout
+
+	var buffer bytes.Buffer
+	_, _ = buffer.ReadFrom(r)
+	got := strings.TrimSpace(buffer.String())
+
+	if got != expected {
+		t.Errorf("PartTwo() printed %q, want %q", got, expected)
+	}
+}

internal/2018/DayFive/code.go

@@ -0,0 +1,64 @@
+package dayfive
+
+import (
+	"advent-of-code/internal/registry"
+	"os"
+	"unicode"
+)
+
+func init() {
+	registry.Register("2018D5", ParseInput, PartOne, PartTwo)
+}
+
+func ParseInput(filepath string) string {
+	content, _ := os.ReadFile(filepath)
+	return string(content)
+}
+
+func reactPolymer(data string) int {
+	stack := []rune{}
+
+	for _, char := range data {
+		if len(stack) == 0 {
+			stack = append(stack, char)
+			continue
+		}
+
+		top := stack[len(stack)-1]
+
+		if unicode.ToLower(top) == unicode.ToLower(char) && top != char {
+			stack = stack[:len(stack)-1]
+		} else {
+			stack = append(stack, char)
+		}
+	}
+
+	return len(stack)
+}
+
+func PartOne(data string) int {
+	return reactPolymer(data)
+}
+
+func PartTwo(data string) int {
+	unitTypes := make(map[rune]bool)
+	for _, char := range data {
+		unitTypes[unicode.ToLower(char)] = true
+	}
+
+	shortestPolymerLength := len(data)
+	for unitType := range unitTypes {
+		filtered := make([]rune, 0, len(data))
+		for _, char := range data {
+			if unicode.ToLower(char) != unitType {
+				filtered = append(filtered, char)
+			}
+		}
+		length := reactPolymer(string(filtered))
+		if length < shortestPolymerLength {
+			shortestPolymerLength = length
+		}
+	}
+
+	return shortestPolymerLength
+}

internal/2018/DayFive/code_test.go

@@ -0,0 +1,21 @@
+package dayfive
+
+import "testing"
+
+var testInput = "dabAcCaCBAcCcaDA"
+
+func TestPartOne(t *testing.T) {
+	expected := 10
+	got := PartOne(testInput)
+	if got != expected {
+		t.Errorf("PartOne() = %d, want %d", got, expected)
+	}
+}
+
+func TestPartTwo(t *testing.T) {
+	expected := 4
+	got := PartTwo(testInput)
+	if got != expected {
+		t.Errorf("PartTwo() = %d, want %d", got, expected)
+	}
+}

internal/2018/register.go

@@ -1,6 +1,7 @@
 package year2018
 
 import (
+	_ "advent-of-code/internal/2018/DayFive"
 	_ "advent-of-code/internal/2018/DayFour"
 	_ "advent-of-code/internal/2018/DayOne"
 	_ "advent-of-code/internal/2018/DayThree"

internal/data/2015/DayFourteen/input.txt

@@ -0,0 +1,9 @@
+Vixen can fly 19 km/s for 7 seconds, but then must rest for 124 seconds.
+Rudolph can fly 3 km/s for 15 seconds, but then must rest for 28 seconds.
+Donner can fly 19 km/s for 9 seconds, but then must rest for 164 seconds.
+Blitzen can fly 19 km/s for 9 seconds, but then must rest for 158 seconds.
+Comet can fly 13 km/s for 7 seconds, but then must rest for 82 seconds.
+Cupid can fly 25 km/s for 6 seconds, but then must rest for 145 seconds.
+Dasher can fly 14 km/s for 3 seconds, but then must rest for 38 seconds.
+Dancer can fly 3 km/s for 16 seconds, but then must rest for 37 seconds.
+Prancer can fly 25 km/s for 6 seconds, but then must rest for 143 seconds.