Day 10. part 2.

day_10/example_data_04.txt

@@ -0,0 +1,6 @@
+012345
+123456
+234567
+345678
+4.6789
+56789.

day_10/solution.go

@@ -41,7 +41,17 @@ func SolveBasic(input string) int {
 
 // task:https://adventofcode.com/2024/day/10#part2
 func SolveComplex(input string) int {
-	return 0
+	topographicMap := loadMap(input)
+	solutions := 0
+	for y, line := range topographicMap {
+		for x, pos := range line {
+			if pos == '0' {
+				trails := rating(topographicMap, x, y)
+				solutions += trails
+			}
+		}
+	}
+	return solutions
 }
 
 func score(tMap TopographicMap, x int, y int) int {
@@ -71,6 +81,33 @@ func score(tMap TopographicMap, x int, y int) int {
 	return len(trails)
 }
 
+func rating(tMap TopographicMap, x int, y int) int {
+	queue := []Point{{x, y, '0'}}
+	trails := 0
+	for len(queue) > 0 {
+		p := queue[0]
+		queue = queue[1:]
+
+		if p.height == '9' {
+			trails++
+		} else {
+			if tMap.At(p.x-1, p.y) == p.height+1 {
+				queue = append(queue, Point{p.x - 1, p.y, p.height + 1})
+			}
+			if tMap.At(p.x, p.y-1) == p.height+1 {
+				queue = append(queue, Point{p.x, p.y - 1, p.height + 1})
+			}
+			if tMap.At(p.x+1, p.y) == p.height+1 {
+				queue = append(queue, Point{p.x + 1, p.y, p.height + 1})
+			}
+			if tMap.At(p.x, p.y+1) == p.height+1 {
+				queue = append(queue, Point{p.x, p.y + 1, p.height + 1})
+			}
+		}
+	}
+	return trails
+}
+
 func loadMap(input string) TopographicMap {
 	input = strings.ReplaceAll(input, "\r", "")
 	topographicMap := TopographicMap{}

day_10/solution_test.go

@@ -18,6 +18,9 @@ var ExampleData02 string
 //go:embed example_data_03.txt
 var ExampleData03 string
 
+//go:embed example_data_04.txt
+var ExampleData04 string
+
 func TestBasicSolutionExample(t *testing.T) {
 	result := day_10.SolveBasic(ExampleData)
 	if result != 36 {
@@ -48,7 +51,21 @@ func TestBasicSolutionExample03(t *testing.T) {
 
 func TestComplexSolutionExample(t *testing.T) {
 	result := day_10.SolveComplex(ExampleData)
-	if result != 2858 {
-		t.Fatalf("Expected 2858 received %d", result)
+	if result != 81 {
+		t.Fatalf("Expected 81 received %d", result)
+	}
+}
+
+func TestComplexSolutionExample03(t *testing.T) {
+	result := day_10.SolveComplex(ExampleData03)
+	if result != 13 {
+		t.Fatalf("Expected 13 received %d", result)
+	}
+}
+
+func TestComplexSolutionExample04(t *testing.T) {
+	result := day_10.SolveComplex(ExampleData04)
+	if result != 227 {
+		t.Fatalf("Expected 227 received %d", result)
 	}
 }