Day 10: Part 1 and 2

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

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())
+}