d6

d6/d6.go

@@ -0,0 +1,59 @@
+package d6
+
+import (
+	"strconv"
+	"strings"
+)
+
+func toNum(in []string) []int {
+	nums := make([]int, 0, len(in))
+
+	for idx, str := range in {
+		num, _ := strconv.Atoi(str)
+		nums[idx] = num
+	}
+
+	return nums
+}
+
+func D6(input string, startDays int) int {
+	fishes := toNum(strings.Split(strings.TrimSpace(input), ","))
+
+	for day := 0; day < startDays; day++ {
+		for idx := range fishes {
+			if fishes[idx] == 0 {
+				fishes[idx] = 6
+				fishes = append(fishes, 8)
+			} else {
+				fishes[idx]--
+			}
+		}
+	}
+
+	return len(fishes)
+}
+
+// Inspired by
+// https://www.reddit.com/r/adventofcode/comments/r9z49j/comment/hnfaisu/?utm_source=share&utm_medium=web2x&context=3
+func D6P2(input string, startDays int) int {
+	fishes := toNum(strings.Split(strings.TrimSpace(input), ","))
+	ages := make([]int, 9)
+
+	for _, fish := range fishes {
+		ages[fish]++
+	}
+
+	for day := 0; day < startDays; day++ {
+		dieToday := ages[0]
+		ages = ages[1:]
+		ages[6] += dieToday
+		ages = append(ages, dieToday)
+	}
+
+	sum := 0
+	for _, age := range ages {
+		sum += age
+	}
+
+	return sum
+}

d6/d6_test.go

@@ -0,0 +1,19 @@
+package d6
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestD6(t *testing.T) {
+	assert.EqualValues(t, 5934, D6("3,4,3,1,2", 80))
+}
+
+func TestD6P2Naive(t *testing.T) {
+	assert.EqualValues(t, 26984457539, D6("3", 256))
+}
+
+func TestD6P2(t *testing.T) {
+	assert.EqualValues(t, 26984457539, D6P2("3,4,3,1,2", 256))
+}

main.go

@@ -12,6 +12,7 @@ import (
 	"github.com/fotonmoton/aoc2021/d3"
 	"github.com/fotonmoton/aoc2021/d4"
 	"github.com/fotonmoton/aoc2021/d5"
+	"github.com/fotonmoton/aoc2021/d6"
 )
 
 func main() {
@@ -34,4 +35,6 @@ func main() {
 	fmt.Printf("day 4 part 2: %v\n", d4.D4P2(client.Day(4)))
 	fmt.Printf("day 5: %v\n", d5.D5(client.Day(5)))
 	fmt.Printf("day 5 part 2: %v\n", d5.D5P2(client.Day(5)))
+	fmt.Printf("day 6: %v\n", d6.D6(client.Day(6), 80))
+	fmt.Printf("day 6 part 2: %v\n", d6.D6P2(client.Day(6), 256))
 }