Day 12. part 2.

day_12/example_data_01.txt

@@ -0,0 +1,4 @@
+AAAA
+BBCD
+BBCC
+EEEC

day_12/solution.go

@@ -23,6 +23,11 @@ func (m Map) At(x, y int) rune {
 	return Empty
 }
 
+func (v Visited) At(x, y int) bool {
+	_, visited := v[Point{x, y}]
+	return visited
+}
+
 // task:https://adventofcode.com/2024/day/12
 func SolveBasic(input string) int {
 	farmMap := loadMap(input)
@@ -55,6 +60,7 @@ func SolveBasic(input string) int {
 						parameter++
 					}
 				}
+
 				sum += area * parameter
 			}
 		}
@@ -63,6 +69,84 @@ func SolveBasic(input string) int {
 	return sum
 }
 
+// task:https://adventofcode.com/2024/day/12#part2
+func SolveComplex(input string) int {
+	farmMap := loadMap(input)
+	visited := Visited{}
+
+	sum := 0
+
+	for y, row := range farmMap {
+		for x, value := range row {
+			p := Point{x, y}
+			field := Visited{}
+			if _, present := visited[p]; !present {
+				visit(farmMap, field, x, y, value)
+				area := len(field)
+				parameter := countEdges(farmMap, field)
+
+				for point := range field {
+					// mark as visited to not visit it more than once
+					visited[point] = true
+				}
+				sum += area * parameter
+			}
+		}
+	}
+	return sum
+}
+
+func countEdges(farmMap Map, field Visited) int {
+	borders := map[BorderPoint]bool{}
+	edges := 0
+
+	for y, row := range farmMap {
+		for x := range row {
+			if field.At(x, y) {
+				if !field.At(x-1, y) {
+					if !borders[BorderPoint{x, y - 1, LEFT}] {
+						edges++
+					}
+					borders[BorderPoint{x, y, LEFT}] = true
+				}
+				if !field.At(x, y-1) {
+					if !borders[BorderPoint{x - 1, y, TOP}] {
+						edges++
+					}
+					borders[BorderPoint{x, y, TOP}] = true
+				}
+				if !field.At(x, y+1) {
+					if !borders[BorderPoint{x - 1, y, BOTTOM}] {
+						edges++
+					}
+					borders[BorderPoint{x, y, BOTTOM}] = true
+				}
+				if !field.At(x+1, y) {
+					if !borders[BorderPoint{x, y - 1, RIGHT}] {
+						edges++
+					}
+					borders[BorderPoint{x, y, RIGHT}] = true
+				}
+			}
+		}
+	}
+	return edges
+}
+
+type Direction int
+
+const (
+	LEFT   Direction = iota
+	TOP    Direction = iota
+	RIGHT  Direction = iota
+	BOTTOM Direction = iota
+)
+
+type BorderPoint struct {
+	x, y      int
+	direction Direction
+}
+
 func visit(farmMap Map, field Visited, x int, y int, value rune) {
 	if _, visited := field[Point{x, y}]; visited {
 		return
@@ -77,11 +161,6 @@ func visit(farmMap Map, field Visited, x int, y int, value rune) {
 	}
 }
 
-// task:https://adventofcode.com/2024/day/12#part2
-func SolveComplex(input string) int {
-	return 0
-}
-
 func loadMap(input string) Map {
 	input = strings.ReplaceAll(input, "\r", "")
 	topographicMap := Map{}

day_12/solution_test.go

@@ -9,6 +9,9 @@ import (
 //go:embed example_data.txt
 var ExampleData string
 
+//go:embed example_data_01.txt
+var ExampleData01 string
+
 func TestBasicSolutionExample(t *testing.T) {
 	result := day_12.SolveBasic(ExampleData)
 	if result != 1930 {
@@ -18,7 +21,14 @@ func TestBasicSolutionExample(t *testing.T) {
 
 func TestComplexSolutionExample(t *testing.T) {
 	result := day_12.SolveComplex(ExampleData)
-	if result != 2858 {
-		t.Fatalf("Expected 2858 received %d", result)
+	if result != 1206 {
+		t.Fatalf("Expected 1206 received %d", result)
+	}
+}
+
+func TestComplexSolutionExample01(t *testing.T) {
+	result := day_12.SolveComplex(ExampleData01)
+	if result != 80 {
+		t.Fatalf("Expected 80 received %d", result)
 	}
 }