Day 6 solution

README.md

@@ -65,3 +65,13 @@ There are 5585 overlapping vents
 There are 17193 overlapping vents
 ```
 
+
+### Day six
+
+```sh
+$ ./aoc2021 --six
+The solution for "six" is:
+After 80 days there are 377263 fish
+After 256 days there are 1695929023803 fish
+```
+

main.go

@@ -8,6 +8,7 @@ import (
 	"unsupervised.ca/aoc2021/five"
 	"unsupervised.ca/aoc2021/four"
 	"unsupervised.ca/aoc2021/one"
+	"unsupervised.ca/aoc2021/six"
 	"unsupervised.ca/aoc2021/three"
 	"unsupervised.ca/aoc2021/two"
 )
@@ -37,6 +38,8 @@ func main() {
 		day = four.Init("four/input.txt")
 	case "five":
 		day = five.Init("five/input.txt")
+	case "six":
+		day = six.Init("six/input.txt")
 	default:
 		fmt.Printf("%q does not have a solution.\n", flagParts[1])
 		help()

six/input.txt

@@ -0,0 +1 @@
+5,1,1,5,4,2,1,2,1,2,2,1,1,1,4,2,2,4,1,1,1,1,1,4,1,1,1,1,1,5,3,1,4,1,1,1,1,1,4,1,5,1,1,1,4,1,2,2,3,1,5,1,1,5,1,1,5,4,1,1,1,4,3,1,1,1,3,1,5,5,1,1,1,1,5,3,2,1,2,3,1,5,1,1,4,1,1,2,1,5,1,1,1,1,5,4,5,1,3,1,3,3,5,5,1,3,1,5,3,1,1,4,2,3,3,1,2,4,1,1,1,1,1,1,1,2,1,1,4,1,3,2,5,2,1,1,1,4,2,1,1,1,4,2,4,1,1,1,1,4,1,3,5,5,1,2,1,3,1,1,4,1,1,1,1,2,1,1,4,2,3,1,1,1,1,1,1,1,4,5,1,1,3,1,1,2,1,1,1,5,1,1,1,1,1,3,2,1,2,4,5,1,5,4,1,1,3,1,1,5,5,1,3,1,1,1,1,4,4,2,1,2,1,1,5,1,1,4,5,1,1,1,1,1,1,1,1,1,1,3,1,1,1,1,1,4,2,1,1,1,2,5,1,4,1,1,1,4,1,1,5,4,4,3,1,1,4,5,1,1,3,5,3,1,2,5,3,4,1,3,5,4,1,3,1,5,1,4,1,1,4,2,1,1,1,3,2,1,1,4

six/lanternfish.go

@@ -0,0 +1,65 @@
+package six
+
+import (
+	"bufio"
+	"os"
+	"strconv"
+	"strings"
+)
+
+type lanternfish struct {
+	fish       map[int]int
+	population int
+}
+
+func (l *lanternfish) load(filename string) error {
+	file, err := os.Open(filename)
+	if err != nil {
+		return err
+	}
+	defer file.Close()
+	scanner := bufio.NewScanner(file)
+	l.fish = map[int]int{}
+	for scanner.Scan() {
+		fishes := strings.Split(scanner.Text(), ",")
+		for _, fishy := range fishes {
+			f, err := strconv.Atoi(fishy)
+			if err != nil {
+				return err
+			}
+
+			l.fish[f]++
+		}
+	}
+
+	for _, count := range l.fish {
+		l.population += count
+	}
+
+	return nil
+}
+
+func (l *lanternfish) simulate(days int) {
+	for i := 0; i < days; i++ {
+		// How many fish spawn today
+		newFish := l.fish[0]
+
+		// Advance spawn counts
+		for j := 0; j < 8; j++ {
+			l.fish[j] = l.fish[j+1]
+		}
+
+		// Reset spawning fish to 6 days
+		l.fish[6] += newFish
+
+		// Add new fish to day 8
+		l.fish[8] = newFish
+
+		population := 0
+		for _, count := range l.fish {
+			population += count
+		}
+
+		l.population = population
+	}
+}

six/lanternfish_test.go

@@ -0,0 +1,44 @@
+package six
+
+import "testing"
+
+func Test_read(t *testing.T) {
+	l := lanternfish{}
+	if err := l.load("test_input.txt"); err != nil {
+		t.Log(err)
+		t.FailNow()
+	}
+
+	if l.population != 5 {
+		t.Logf("Expected 5 fish, found %d", l.population)
+		t.Fail()
+	}
+}
+
+func Test_simulate(t *testing.T) {
+	l := lanternfish{}
+	l.load("test_input.txt")
+
+	l.simulate(18)
+	if l.population != 26 {
+		t.Logf("Expected 26 fish, found %d", l.population)
+		t.Fail()
+	}
+
+	l.simulate(62)
+	if l.population != 5934 {
+		t.Logf("Expected 5934 fish, found %d", l.population)
+		t.Fail()
+	}
+}
+
+func Test_simulateForever(t *testing.T) {
+	l := lanternfish{}
+	l.load("test_input.txt")
+
+	l.simulate(256)
+	if l.population != 26984457539 {
+		t.Logf("Expected 26984457539 fish, found %d", l.population)
+		t.Fail()
+	}
+}

six/main.go

@@ -0,0 +1,26 @@
+package six
+
+import "fmt"
+
+type Six struct {
+	lanternfish lanternfish
+}
+
+func Init(filepath string) *Six {
+	six := &Six{
+		lanternfish: lanternfish{},
+	}
+
+	six.lanternfish.load(filepath)
+	return six
+}
+
+func (d *Six) Answer() string {
+	d.lanternfish.simulate(80)
+	return fmt.Sprintf("After 80 days there are %d fish", d.lanternfish.population)
+}
+
+func (d *Six) FollowUp() string {
+	d.lanternfish.simulate(176)
+	return fmt.Sprintf("After 256 days there are %d fish", d.lanternfish.population)
+}

six/test_input.txt

@@ -0,0 +1 @@
+3,4,3,1,2