Day 10: Part 1 and 2

Signed-off-by: James Griffin <james@unsupervised.ca>

main.go

@@ -3,7 +3,7 @@ package main
 import (
 	"fmt"
 
-	"github.com/thatguygriff/aoc2020/nine"
+	"github.com/thatguygriff/aoc2020/ten"
 )
 
 func main() {
@@ -40,6 +40,10 @@ func main() {
 	// fmt.Println(eight.PartTwo())
 
 	// Day 9
-	fmt.Println(nine.PartOne())
+	// fmt.Println(nine.PartOne())
-	fmt.Println(nine.PartTwo())
+	// fmt.Println(nine.PartTwo())
+
+	// Day 10
+	fmt.Println(ten.PartOne())
+	fmt.Println(ten.PartTwo())
 }

ten/day_ten.go

@@ -0,0 +1,119 @@
+package ten
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"sort"
+	"strconv"
+)
+
+func newBag(f string) *bag {
+	b := &bag{}
+	b.load(f)
+	return b
+}
+
+type adapter struct {
+	output int
+}
+
+type bag struct {
+	adapters []adapter
+}
+
+func (b *bag) load(filename string) error {
+	file, err := os.Open(filename)
+	if err != nil {
+		return err
+	}
+	defer file.Close()
+
+	scanner := bufio.NewScanner(file)
+	for scanner.Scan() {
+		v, err := strconv.Atoi(scanner.Text())
+		if err != nil {
+			return err
+		}
+		b.adapters = append(b.adapters, adapter{
+			output: v,
+		})
+	}
+
+	return nil
+}
+
+func (b *bag) distribution() (one, two, three int, err error) {
+	if len(b.adapters) == 0 {
+		return one, two, three, nil
+	}
+	sort.SliceStable(b.adapters, func(i, j int) bool { return b.adapters[i].output < b.adapters[j].output })
+
+	current := 0
+	for i := 0; i < len(b.adapters); i++ {
+		next := b.adapters[i].output
+		switch next - current {
+		case 1:
+			one++
+		case 2:
+			two++
+		case 3:
+			three++
+		default:
+			return one, two, three, fmt.Errorf("Unsupported joltage difference %d", b.adapters[i+1].output-b.adapters[i].output)
+		}
+		current = next
+	}
+	// The device is always 3 higher
+	three++
+
+	return one, two, three, nil
+}
+
+func (b *bag) countArrangements() int {
+	if len(b.adapters) == 0 {
+		return 0
+	}
+	sort.SliceStable(b.adapters, func(i, j int) bool { return b.adapters[i].output < b.adapters[j].output })
+
+	// Pilfered from reddit after beating my head against a wall not getting the looping correct
+	outputs := []int{0}
+	for _, a := range b.adapters {
+		outputs = append(outputs, a.output)
+	}
+	outputs = append(outputs, outputs[len(outputs)-1]+3)
+
+	dp := make([]int, len(outputs))
+
+	dp[0] = 1
+	dp[1] = 1
+
+	for i := 2; i < len(dp); i++ {
+		for j := i - 1; j >= 0; j-- {
+			if outputs[i]-outputs[j] <= 3 {
+				dp[i] += dp[j]
+			} else {
+				break
+			}
+		}
+	}
+
+	return dp[len(dp)-1]
+}
+
+// PartOne Find the jolt difference product
+func PartOne() string {
+	b := newBag("ten/input.txt")
+	one, two, three, err := b.distribution()
+	if err != nil {
+		return fmt.Sprintf("Unable to find a distribution: %v", err)
+	}
+
+	return fmt.Sprintf("Got %d, %d, %d jolts differences with a %d product", one, two, three, one*three)
+}
+
+// PartTwo Find the number of arrangements of adapters
+func PartTwo() string {
+	b := newBag("ten/input.txt")
+	return fmt.Sprintf("Found %d possible arrangements", b.countArrangements())
+}

ten/day_ten_test.go

@@ -0,0 +1,71 @@
+package ten
+
+import "testing"
+
+func Test_program_load(t *testing.T) {
+	b := bag{}
+	err := b.load("sample1.txt")
+	if err != nil {
+		t.Log(err)
+		t.FailNow()
+	}
+
+	if len(b.adapters) != 11 {
+		t.Logf("Expected 11 adapters, Got %d adapters", len(b.adapters))
+		t.FailNow()
+	}
+}
+
+func Test_distribution_sample1(t *testing.T) {
+	b := bag{}
+	b.load("sample1.txt")
+
+	one, two, three, err := b.distribution()
+	if err != nil {
+		t.Logf(err.Error())
+		t.FailNow()
+	}
+
+	if one != 7 || two != 0 || three != 5 {
+		t.Logf("Expected 7, 0, 5 jolt diffs, Got %d, %d, %d jolts", one, two, three)
+		t.FailNow()
+	}
+}
+
+func Test_distribution_sample2(t *testing.T) {
+	b := bag{}
+	b.load("sample2.txt")
+
+	one, two, three, err := b.distribution()
+	if err != nil {
+		t.Logf(err.Error())
+		t.FailNow()
+	}
+
+	if one != 22 || two != 0 || three != 10 {
+		t.Logf("Expected 22, 0, 10 jolt diffs, Got %d, %d, %d jolts", one, two, three)
+		t.FailNow()
+	}
+}
+
+func Test_arrangement_sample1(t * testing.T) {
+	b := newBag("sample1.txt")
+
+	count := b.countArrangements()
+
+	if count != 8 {
+		t.Logf("Expected 8 arrangments, got %d", count)
+		t.FailNow()
+	}
+}
+
+func Test_arrangement_sample2(t * testing.T) {
+	b := newBag("sample2.txt")
+
+	count := b.countArrangements()
+
+	if count != 19208 {
+		t.Logf("Expected 19208 arrangments, got %d", count)
+		t.FailNow()
+	}
+}

ten/input.txt

@@ -0,0 +1,107 @@
+48
+171
+156
+51
+26
+6
+80
+62
+65
+82
+130
+97
+49
+31
+142
+83
+75
+20
+154
+119
+56
+114
+92
+33
+140
+74
+118
+1
+96
+44
+128
+134
+121
+64
+158
+27
+17
+101
+59
+12
+89
+88
+145
+167
+11
+3
+39
+43
+105
+16
+170
+63
+111
+2
+108
+21
+146
+77
+45
+52
+32
+127
+147
+76
+58
+37
+86
+129
+57
+133
+120
+163
+138
+161
+139
+71
+9
+141
+168
+164
+124
+157
+95
+25
+38
+69
+87
+155
+135
+15
+102
+70
+34
+42
+24
+50
+68
+169
+10
+55
+117
+30
+81
+151
+100
+162
+148

ten/sample1.txt

@@ -0,0 +1,11 @@
+16
+10
+15
+5
+1
+11
+7
+19
+6
+12
+4

ten/sample2.txt

@@ -0,0 +1,31 @@
+28
+33
+18
+42
+31
+14
+46
+20
+48
+47
+24
+23
+49
+45
+19
+38
+39
+11
+1
+32
+25
+35
+8
+17
+7
+9
+4
+2
+34
+10
+3