feat: solve part two using exhaustive search

internal/2015/DayFourteen/code.go

@@ -8,15 +8,19 @@ import (
 	"strings"
 )
 
-func init() {
-	registry.Register("2015D14", ParseInput, PartOne, PartTwo)
-}
+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
-	CycleTime int
+	Points   int
+}
+
+func init() {
+	registry.Register("2015D14", ParseInput, PartOne, PartTwo)
 }
 
 func ParseInput(filepath string) []string {
@@ -24,28 +28,37 @@ func ParseInput(filepath string) []string {
 	return strings.Split(string(content), "\n")
 }
 
-func calculateMaxDistance(data []string, time int) int {
-	maxDistance := 0
-	pattern := regexp.MustCompile(`\w+ can fly (\d+) km/s for (\d+) seconds, but then must rest for (\d+) seconds\.`)
-
-	for _, line := range data {
-		matches := pattern.FindStringSubmatch(line)
-		var reindeer Reindeer
-		reindeer.Speed, _ = strconv.Atoi(matches[1])
-		reindeer.FlyTime, _ = strconv.Atoi(matches[2])
-		reindeer.RestTime, _ = strconv.Atoi(matches[3])
-		reindeer.CycleTime = reindeer.FlyTime + reindeer.RestTime
-
-		fullCycles := time / reindeer.CycleTime
-		distance := fullCycles * reindeer.Speed * reindeer.FlyTime
-
-		remainingTime := time % reindeer.CycleTime
-		if remainingTime > reindeer.FlyTime {
-			distance += reindeer.Speed * reindeer.FlyTime
-		} else {
-			distance += reindeer.Speed * remainingTime
+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
 		}
@@ -54,10 +67,42 @@ func calculateMaxDistance(data []string, time int) int {
 	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, 2503)
+	return calculateMaxDistance(data, raceTime)
 }
 
 func PartTwo(data []string) int {
-	return 0
+	return calculateMaxPoints(data, raceTime)
 }

internal/2015/DayFourteen/code_test.go

@@ -14,3 +14,11 @@ func TestPartOne(t *testing.T) {
 		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/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"