Day 16: Part 2

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

main.go

@@ -69,4 +69,5 @@ func main() {
 
 	// Day 16
 	fmt.Println(sixteen.PartOne())
+	fmt.Println(sixteen.PartTwo())
 }

sixteen/day_sixteen.go

@@ -10,17 +10,21 @@ import (
 
 type ticket struct {
 	values []int
-	fields []string
 }
 
 type constraint struct {
 	min, max int
 }
 
+type constraints []constraint
+
 type ticketScanner struct {
-	rules  map[string][]constraint
+	rules  map[string]constraints
 	me     *ticket
 	nearby []ticket
+	valid  []ticket
+
+	fields []string
 }
 
 func (ts *ticketScanner) load(filename string) error {
@@ -30,7 +34,7 @@ func (ts *ticketScanner) load(filename string) error {
 	}
 	defer file.Close()
 
-	ts.rules = make(map[string][]constraint)
+	ts.rules = make(map[string]constraints)
 	var rules, myticket bool
 	scanner := bufio.NewScanner(file)
 	for scanner.Scan() {
@@ -95,19 +99,23 @@ func (ts *ticketScanner) load(filename string) error {
 	return nil
 }
 
+func (c *constraints) valid(input int) bool {
+	for _, r := range *c {
+		if input >= r.min && input <= r.max {
+			return true
+		}
+	}
+	return false
+}
+
 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 {
+				if rule.valid(value) {
+					valid = true
 					break
 				}
 			}
@@ -120,6 +128,109 @@ func (ts *ticketScanner) nearbyErrorRate() int {
 	return errorRate
 }
 
+func (ts *ticketScanner) scanValid() {
+	for _, t := range ts.nearby {
+		validTicket := true
+		for _, v := range t.values {
+			validValue := false
+			for _, r := range ts.rules {
+				if r.valid(v) {
+					validValue = true
+					break
+				}
+			}
+			if !validValue {
+				validTicket = false
+				break
+			}
+		}
+		if validTicket {
+			ts.valid = append(ts.valid, t)
+		}
+	}
+}
+
+func (ts *ticketScanner) determineFields() {
+	ts.fields = make([]string, len(ts.rules))
+
+	possibilities := map[string][]int{}
+	for name, r := range ts.rules {
+		possibilities[name] = []int{}
+
+		for i := 0; i < len(ts.fields); i++ {
+			isValid := true
+			for j := 0; j < len(ts.valid); j++ {
+				if !r.valid(ts.valid[j].values[i]) {
+					isValid = false
+				}
+			}
+			if isValid {
+				possibilities[name] = append(possibilities[name], i)
+			}
+		}
+	}
+
+	for i := 0; i < len(ts.fields); i++ {
+		if ts.fields[i] != "" {
+			continue
+		}
+		options := []string{}
+		for name, indexes := range possibilities {
+			for _, index := range indexes {
+				if i == index {
+					options = append(options, name)
+				}
+			}
+		}
+
+		if len(options) == 1 {
+			ts.fields[i] = options[0]
+			possibilities = removeIndex(i, options[0], possibilities)
+			continue
+		}
+
+		min := len(ts.fields)
+		minKey := ""
+		for _, option := range options {
+			if len(possibilities[option]) < min {
+				min = len(possibilities[option])
+				minKey = option
+			}
+		}
+		ts.fields[i] = minKey
+		possibilities = removeIndex(i, minKey, possibilities)
+	}
+}
+
+func removeIndex(index int, used string, possibilities map[string][]int) map[string][]int {
+	updatedPossibilites := make(map[string][]int)
+	for key, indexes := range possibilities {
+		if used == key {
+			continue
+		}
+		updatedIndexes := []int{}
+		for _, i := range indexes {
+			if i != index {
+				updatedIndexes = append(updatedIndexes, i)
+			}
+		}
+
+		updatedPossibilites[key] = updatedIndexes
+	}
+	return updatedPossibilites
+}
+
+func (ts *ticketScanner) fieldProduct(prefix string) int {
+	product := 1
+	for i, f := range ts.fields {
+		if strings.Contains(f, prefix) {
+			product *= ts.me.values[i]
+		}
+	}
+
+	return product
+}
+
 // PartOne What is my nearby ticket scanning error rate
 func PartOne() string {
 	ts := ticketScanner{}
@@ -129,3 +240,16 @@ func PartOne() string {
 
 	return fmt.Sprintf("The nearby scanning error rate is %d", ts.nearbyErrorRate())
 }
+
+// PartTwo What is the product of all fields beginning with "departure"
+func PartTwo() string {
+	ts := ticketScanner{}
+	if err := ts.load("sixteen/input.txt"); err != nil {
+		return err.Error()
+	}
+
+	ts.scanValid()
+	ts.determineFields()
+
+	return fmt.Sprintf("The product of departure is %d", ts.fieldProduct("departure"))
+}

sixteen/day_sixteen_test.go

@@ -24,7 +24,7 @@ func Test_ticket_loading(t *testing.T) {
 		t.Fail()
 	}
 }
-	
+
 func Test_ticket_scanerror(t *testing.T) {
 	ts := ticketScanner{}
 	if err := ts.load("sample.txt"); err != nil {
@@ -38,3 +38,45 @@ func Test_ticket_scanerror(t *testing.T) {
 		t.Fail()
 	}
 }
+
+func Test_ticket_fieldDetection(t *testing.T) {
+	ts := ticketScanner{}
+	if err := ts.load("sample2.txt"); err != nil {
+		t.Log(err.Error())
+		t.FailNow()
+	}
+
+	ts.scanValid()
+	if len(ts.valid) != 3 {
+		t.Logf("Expected 3 valid tickets, got %d", len(ts.valid))
+		t.FailNow()
+	}
+
+	ts.determineFields()
+
+	if len(ts.fields) != 3 || ts.fields[0] != "row" || ts.fields[1] != "class" || ts.fields[2] != "seat" {
+		t.Logf("Expected row, class, seat but got %v", ts.fields)
+		t.Fail()
+	}
+}
+
+func Test_ticket_product(t *testing.T) {
+	ts := ticketScanner{}
+	if err := ts.load("sample3.txt"); err != nil {
+		t.Log(err.Error())
+		t.FailNow()
+	}
+
+	ts.scanValid()
+	if len(ts.valid) != 3 {
+		t.Logf("Expected 3 valid tickets, got %d", len(ts.valid))
+		t.FailNow()
+	}
+
+	ts.determineFields()
+	p := ts.fieldProduct("departure")
+	if p != 132 {
+		t.Logf("Expected 132 got %d", p)
+		t.Fail()
+	}
+}

sixteen/sample2.txt

@@ -0,0 +1,11 @@
+class: 0-1 or 4-19
+row: 0-5 or 8-19
+seat: 0-13 or 16-19
+
+your ticket:
+11,12,13
+
+nearby tickets:
+3,9,18
+15,1,5
+5,14,9

sixteen/sample3.txt

@@ -0,0 +1,11 @@
+departure class: 0-1 or 4-19
+departure row: 0-5 or 8-19
+arrival seat: 0-13 or 16-19
+
+your ticket:
+11,12,13
+
+nearby tickets:
+3,9,18
+15,1,5
+5,14,9