feat: solve day nine part 1

README.md

@@ -34,7 +34,7 @@ go test ./cmd/01
 | 06  | [Problem](https://adventofcode.com/2025/day/6)  | [Solution](./cmd/06/) | Part 1 I don't think it is the best solution, but it does solve it. I kicked ass on part 2. 🥳                                                                                                                                              |
 | 07  | [Problem](https://adventofcode.com/2025/day/7)  | [Solution](./cmd/07/) | FIFO for life. 🤣. Fuck me...part 2 I found really difficult and the use of DFS was obvious, but doing the memoizing was not.                                                                                                               |
 | 08  | [Problem](https://adventofcode.com/2025/day/8)  | [Solution](./cmd/08/) | Part 1 had me down bad. I was on the right track with my original solution, but ended up doing it in a brute force way then figuring out my mistake with the original. Fuck this guy. Part 2 was so much easier once part 1 was sorted out. |
-| 09  | [Problem](https://adventofcode.com/2025/day/9)  | [Solution](./cmd/09/) |                                                                                                                                                                                                                                             |
+| 09  | [Problem](https://adventofcode.com/2025/day/9)  | [Solution](./cmd/09/) | Part 1 was such a nice break from the madness of day 8.                                                                                                                                                                                     |
 | 10  | [Problem](https://adventofcode.com/2025/day/10) | [Solution](./cmd/10/) |                                                                                                                                                                                                                                             |
 | 11  | [Problem](https://adventofcode.com/2025/day/11) | [Solution](./cmd/11/) |                                                                                                                                                                                                                                             |
 | 12  | [Problem](https://adventofcode.com/2025/day/12) | [Solution](./cmd/12/) |                                                                                                                                                                                                                                             |

cmd/09/main.go

@@ -0,0 +1,48 @@
+package main
+
+import (
+	"math"
+	"strconv"
+	"strings"
+
+	"github.com/StevanFreeborn/advent-of-code-2025/internal/file"
+)
+
+func SolvePartOne(filePath string) int {
+	points := []struct {
+		x int
+		y int
+	}{}
+
+	for line := range file.ReadLines(filePath) {
+		parts := strings.Split(line, ",")
+		x, _ := strconv.Atoi(parts[0])
+		y, _ := strconv.Atoi(parts[1])
+		p := struct {
+			x int
+			y int
+		}{x: x, y: y}
+		points = append(points, p)
+	}
+
+	numberOfPoints := len(points)
+	largestArea := 0
+
+	for i := range numberOfPoints {
+		for j := i + 1; j < numberOfPoints; j++ {
+			start := points[i]
+			end := points[j]
+
+			width := int(math.Abs(float64(end.x-start.x)) + 1)
+			height := int(math.Abs(float64(end.y-start.y)) + 1)
+
+			a := width * height
+
+			if a > largestArea {
+				largestArea = a
+			}
+		}
+	}
+
+	return largestArea
+}

cmd/09/main_test.go

@@ -0,0 +1,27 @@
+package main_test
+
+import (
+	"testing"
+
+	solution "github.com/StevanFreeborn/advent-of-code-2025/cmd/09"
+)
+
+func TestSolvePartOneWithExampleInput(t *testing.T) {
+	expected := 50
+
+	result := solution.SolvePartOne("EXAMPLE.txt")
+
+	if result != expected {
+		t.Errorf("got %d but wanted %d", result, expected)
+	}
+}
+
+func TestSolvePartOneWithInput(t *testing.T) {
+	expected := 4_758_121_828
+
+	result := solution.SolvePartOne("INPUT.txt")
+
+	if result != expected {
+		t.Errorf("got %d but wanted %d", result, expected)
+	}
+}