Day 7: Part 1 and 2

Signed-off-by: James Griffin <james.griffin-allwood@agilebits.com>

seven/day_seven.go

@@ -0,0 +1,147 @@
+package seven
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strings"
+)
+
+type bag struct {
+	colour   string
+	capacity map[string]int
+}
+
+type rules struct {
+	bags []bag
+}
+
+func (r *rules) load(filename string) error {
+	file, err := os.Open(filename)
+	if err != nil {
+		return err
+	}
+	defer file.Close()
+
+	scanner := bufio.NewScanner(file)
+	for scanner.Scan() {
+		var colour, c1, c2 string
+		rule := strings.Split(scanner.Text(), " contain ")
+
+		if len(rule) != 2 {
+			return fmt.Errorf("Unable to parse %s", scanner.Text())
+		}
+
+		found, err := fmt.Sscanf(rule[0], "%s %s bags", &c1, &c2)
+		if err != nil || found != 2 {
+			return fmt.Errorf("Unable to parse colour from %s: %w", rule[0], err)
+		}
+		colour = fmt.Sprintf("%s %s", c1, c2)
+
+		bag := bag{
+			colour:   colour,
+			capacity: make(map[string]int),
+		}
+
+		if rule[1] != "no other bags." {
+			// Trim the trailing period
+			raw := rule[1][:len(rule[1])-1]
+			constraints := strings.Split(raw, ", ")
+
+			for _, c := range constraints {
+				var count int
+				found, err := fmt.Sscanf(c, "%d %s %s bag", &count, &c1, &c2)
+				if err != nil || found != 3 {
+					return fmt.Errorf("Unable to parse colour from %s: %w", c, err)
+				}
+				colour = fmt.Sprintf("%s %s", c1, c2)
+
+				bag.capacity[colour] = count
+			}
+		}
+
+		r.bags = append(r.bags, bag)
+	}
+
+	return nil
+}
+
+func (r *rules) canContain(colours ...string) (int, []string) {
+	holding := []string{}
+
+	for _, c := range colours {
+		for _, b := range r.bags {
+			if _, canHold := b.capacity[c]; canHold {
+				holding = append(holding, b.colour)
+			}
+		}
+	}
+
+	if len(holding) > 0 {
+		_, additional := r.canContain(holding...)
+
+		for _, c := range additional {
+			newColour := true
+			for _, e := range holding {
+				if c == e {
+					newColour = false
+				}
+			}
+			if newColour {
+				holding = append(holding, c)
+			}
+		}
+	}
+
+	return len(holding), holding
+}
+
+func (r *rules) get(colour string) *bag {
+	for _, b := range r.bags {
+		if b.colour == colour {
+			return &b
+		}
+	}
+
+	return nil
+}
+
+func (r *rules) canHold(colour string) int {
+	count := 0
+
+	b := r.get(colour)
+	if b == nil {
+		return count
+	}
+
+	for colour, capcity := range b.capacity {
+		switch r.canHold(colour) {
+		case 0:
+			count += capcity
+		default:
+			count += r.canHold(colour)*capcity + capcity
+		}
+	}
+
+	return count
+}
+
+// PartOne How many bags can hold at least 1 shiny gold
+func PartOne() string {
+	r := rules{}
+	r.load("seven/rules.txt")
+
+	count, _ := r.canContain("shiny gold")
+
+	return fmt.Sprintf("There are %d bags that can hold shiny gold", count)
+}
+
+// PartTwo How many bags must a shiny gold bag hold
+func PartTwo() string {
+	r := rules{}
+	r.load("seven/rules.txt")
+
+	count := r.canHold("shiny gold")
+
+	return fmt.Sprintf("There are %d bags at maximum inside a shiny gold bag", count)
+}