Day 16: Part 1

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

sixteen/day_sixteen.go

@@ -0,0 +1,131 @@
+package sixteen
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+)
+
+type ticket struct {
+	values []int
+	fields []string
+}
+
+type constraint struct {
+	min, max int
+}
+
+type ticketScanner struct {
+	rules  map[string][]constraint
+	me     *ticket
+	nearby []ticket
+}
+
+func (ts *ticketScanner) load(filename string) error {
+	file, err := os.Open(filename)
+	if err != nil {
+		return err
+	}
+	defer file.Close()
+
+	ts.rules = make(map[string][]constraint)
+	var rules, myticket bool
+	scanner := bufio.NewScanner(file)
+	for scanner.Scan() {
+		if scanner.Text() == "" {
+			continue
+		}
+
+		if scanner.Text() == "your ticket:" {
+			rules = true
+			continue
+		}
+
+		if !rules {
+			parts := strings.Split(scanner.Text(), ":")
+			if len(parts) != 2 {
+				return fmt.Errorf("Unable to parse rule %s", scanner.Text())
+			}
+			ranges := []constraint{}
+			c := strings.Split(parts[1], " or ")
+			for _, a := range c {
+				b := constraint{}
+				count, err := fmt.Sscanf(a, "%d-%d", &b.min, &b.max)
+				if count != 2 || err != nil {
+					return fmt.Errorf("Unable to parse %s", a)
+				}
+				ranges = append(ranges, b)
+			}
+			ts.rules[parts[0]] = ranges
+			continue
+		}
+
+		if scanner.Text() == "nearby tickets:" {
+			myticket = true
+			continue
+		}
+
+		if !myticket {
+			t := &ticket{}
+			values := strings.Split(scanner.Text(), ",")
+			for _, v := range values {
+				intValue, err := strconv.Atoi(v)
+				if err != nil {
+					return err
+				}
+				t.values = append(t.values, intValue)
+			}
+			ts.me = t
+			continue
+		}
+
+		t := ticket{}
+		values := strings.Split(scanner.Text(), ",")
+		for _, v := range values {
+			intValue, err := strconv.Atoi(v)
+			if err != nil {
+				return err
+			}
+			t.values = append(t.values, intValue)
+		}
+		ts.nearby = append(ts.nearby, t)
+	}
+	return nil
+}
+
+func (ts *ticketScanner) nearbyErrorRate() int {
+	errorRate := 0
+	for _, t := range ts.nearby {
+		for _, value := range t.values {
+			valid := false
+			for _, rule := range ts.rules {
+				for _, r := range rule {
+					if value >= r.min && value <= r.max {
+						valid = true
+						break
+					}
+				}
+				if valid {
+					break
+				}
+			}
+
+			if !valid {
+				errorRate += value
+			}
+		}
+	}
+	return errorRate
+}
+
+// PartOne What is my nearby ticket scanning error rate
+func PartOne() string {
+	ts := ticketScanner{}
+	if err := ts.load("sixteen/input.txt"); err != nil {
+		return err.Error()
+	}
+
+	return fmt.Sprintf("The nearby scanning error rate is %d", ts.nearbyErrorRate())
+}