Day 19: Part 1 and 2

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

nineteen/day_nineteen.go

@@ -0,0 +1,139 @@
+package nineteen
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+)
+
+type rule struct {
+	matches    string
+	composedOf [][]int
+}
+
+type satellite struct {
+	rules    map[int]rule
+	messages []string
+}
+
+func (s *satellite) load(filename string) error {
+	file, err := os.Open(filename)
+	if err != nil {
+		return err
+	}
+	defer file.Close()
+
+	s.rules = map[int]rule{}
+	scanner := bufio.NewScanner(file)
+	messages := false
+	for scanner.Scan() {
+		if !messages {
+			if scanner.Text() == "" {
+				messages = true
+				continue
+			}
+
+			ruleSplit := strings.Split(scanner.Text(), ": ")
+			ruleKey, err := strconv.Atoi(ruleSplit[0])
+			if err != nil {
+				return err
+			}
+
+			r := rule{}
+
+			if strings.Contains(ruleSplit[1], "\"a\"") {
+				r.matches = "a"
+			} else if strings.Contains(ruleSplit[1], "\"b\"") {
+				r.matches = "b"
+			} else {
+				options := strings.Split(ruleSplit[1], " | ")
+				for _, o := range options {
+					m := []int{}
+					rules := strings.Split(o, " ")
+					for _, r := range rules {
+						t, err := strconv.Atoi(r)
+						if err != nil {
+							return err
+						}
+						m = append(m, t)
+					}
+					r.composedOf = append(r.composedOf, m)
+				}
+			}
+
+			s.rules[ruleKey] = r
+			continue
+		}
+
+		s.messages = append(s.messages, scanner.Text())
+	}
+
+	return nil
+}
+
+func (s *satellite) match(r int, input string) (bool, int) {
+	if len(input) == 0 {
+		return false, 0
+	}
+
+	rule := s.rules[r]
+
+	if rule.matches == string(input[0]) {
+		return true, 1
+	}
+
+	matchedChars := 0
+	for i := 0; i < len(rule.composedOf); i++ {
+		matchedChars = 0
+		valid := true
+		if len(rule.composedOf[i]) > len(input) {
+			continue
+		}
+		for _, sr := range rule.composedOf[i] {
+			match, count := s.match(sr, input[matchedChars:])
+			matchedChars += count
+			if !match {
+				valid = false
+				break
+			}
+		}
+		if valid {
+			return true, matchedChars
+		}
+	}
+
+	return false, matchedChars
+}
+
+func (s *satellite) messageCount(r int) (count int) {
+	for _, m := range s.messages {
+		match, length := s.match(r, m)
+		if match && length == len(m) {
+			count++
+		}
+	}
+
+	return count
+}
+
+// PartOne How many messages match message 0
+func PartOne() string {
+	s := satellite{}
+	if err := s.load("nineteen/input.txt"); err != nil {
+		return err.Error()
+	}
+
+	return fmt.Sprintf("There are %d messages that match rule 0", s.messageCount(0))
+}
+
+// PartTwo How many messages match message 0 with alternate rules
+func PartTwo() string {
+	s := satellite{}
+	if err := s.load("nineteen/input2.txt"); err != nil {
+		return err.Error()
+	}
+
+	return fmt.Sprintf("There are %d messages that match rule 0", s.messageCount(0))
+}