feat: wip on day 9 part 2 solution

cmd/09/main.go

@@ -2,39 +2,35 @@ package main
 
 import (
 	"math"
+	"slices"
 	"strconv"
 	"strings"
 
 	"github.com/StevanFreeborn/advent-of-code-2025/internal/file"
+	"github.com/StevanFreeborn/advent-of-code-2025/internal/position"
 )
 
 func SolvePartOne(filePath string) int {
-	points := []struct {
+	positions := []position.Position{}
-		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 {
+		p := position.From(y, x)
-			x int
+		positions = append(positions, p)
-			y int
-		}{x: x, y: y}
-		points = append(points, p)
 	}
 
-	numberOfPoints := len(points)
+	numberOfPositions := len(positions)
 	largestArea := 0
 
-	for i := range numberOfPoints {
+	for i := range numberOfPositions {
-		for j := i + 1; j < numberOfPoints; j++ {
+		for j := i + 1; j < numberOfPositions; j++ {
-			start := points[i]
+			start := positions[i]
-			end := points[j]
+			end := positions[j]
 
-			width := int(math.Abs(float64(end.x-start.x)) + 1)
+			width := int(math.Abs(float64(end.Column()-start.Column())) + 1)
-			height := int(math.Abs(float64(end.y-start.y)) + 1)
+			height := int(math.Abs(float64(end.Row()-start.Row())) + 1)
 
 			a := width * height
 
@@ -46,3 +42,95 @@ func SolvePartOne(filePath string) int {
 
 	return largestArea
 }
+
+// TODO: How would we construct all the positions
+// in the polygon?
+
+func SolvePartTwo(filePath string) int {
+	positions := []position.Position{}
+
+	for line := range file.ReadLines(filePath) {
+		parts := strings.Split(line, ",")
+		x, _ := strconv.Atoi(parts[0])
+		y, _ := strconv.Atoi(parts[1])
+		p := position.From(y, x)
+		positions = append(positions, p)
+	}
+
+	rowPositions := []int{}
+	columnPositions := []int{}
+
+	for _, positions := range positions {
+		rowPositions = append(rowPositions, positions.Row())
+		columnPositions = append(columnPositions, positions.Column())
+	}
+
+	minRow := slices.Min(rowPositions)
+	maxRow := slices.Max(rowPositions)
+	minCol := slices.Min(columnPositions)
+	maxCol := slices.Max(columnPositions)
+
+	numberOfPositions := len(positions)
+	largestArea := 0
+
+	for i := range numberOfPositions {
+		for j := i + 1; j < numberOfPositions; j++ {
+			start := positions[i]
+			end := positions[j]
+
+			width := int(math.Abs(float64(end.Column()-start.Column())) + 1)
+			height := int(math.Abs(float64(end.Row()-start.Row())) + 1)
+
+			a := width * height
+
+			if a <= largestArea {
+				continue
+			}
+
+			rectMinRow := math.Min(float64(start.Row()), float64(end.Row()))
+			rectMaxRow := math.Max(float64(start.Row()), float64(end.Row()))
+			rectMinCol := math.Min(float64(start.Column()), float64(end.Column()))
+			rectMaxCol := math.Max(float64(start.Column()), float64(end.Column()))
+
+			// is center of rect inside our polygon?
+			centerRow := int((rectMaxRow + rectMinRow) / 2)
+			centerCol := int((rectMaxCol + rectMinCol) / 2)
+			center := position.From(centerRow, centerCol)
+
+			centerIsInside := false
+			j := numberOfPositions - 1
+
+			for i := 0; i < numberOfPositions; i++ {
+				edgeStart := positions[i]
+				edgeEnd := positions[j]
+
+				edgeCoversCenterRow := (edgeStart.Row() > center.Row()) != (edgeEnd.Row() > center.Row())
+
+				edgeHorizontalDistance := edgeEnd.Column() - edgeStart.Column()
+				edgeVeritcalDistance := edgeEnd.Row() - edgeStart.Row()
+				centerVerticalOffset := center.Row() - edgeStart.Row()
+				verticalDistanceCompleted := centerVerticalOffset / edgeVeritcalDistance
+				xIntersection := center.Column() + edgeHorizontalDistance*verticalDistanceCompleted
+				edgeIsToRightOfCenter := center.Column() < xIntersection
+
+				if edgeCoversCenterRow && edgeIsToRightOfCenter {
+					centerIsInside = !centerIsInside
+				}
+
+				j = i
+			}
+
+			if centerIsInside == false {
+				continue
+			}
+
+			// TODO: We need to figure this out
+			// if edges of polygon intersect with
+			// edges of rectangle
+
+			largestArea = a
+		}
+	}
+
+	return largestArea
+}

cmd/09/main_test.go

@@ -25,3 +25,23 @@ func TestSolvePartOneWithInput(t *testing.T) {
 		t.Errorf("got %d but wanted %d", result, expected)
 	}
 }
+
+func TestSolvePartTwoWithExampleInput(t *testing.T) {
+	expected := 24
+
+	result := solution.SolvePartTwo("EXAMPLE.txt")
+
+	if result != expected {
+		t.Errorf("got %d but wanted %d", result, expected)
+	}
+}
+
+func TestSolvePartTwoWithInput(t *testing.T) {
+	expected := -1
+
+	result := solution.SolvePartTwo("INPUT.txt")
+
+	if result != expected {
+		t.Errorf("got %d but wanted %d", result, expected)
+	}
+}

internal/position/position.go

@@ -1,7 +1,11 @@
 // Package position provides types and functions to represent and manipulate positions and moves on a 2D grid.
 package position
 
-import "github.com/StevanFreeborn/advent-of-code-2025/internal/move"
+import (
+	"fmt"
+
+	"github.com/StevanFreeborn/advent-of-code-2025/internal/move"
+)
 
 type Position interface {
 	Row() int
@@ -32,3 +36,7 @@ func (p position) Column() int {
 func (p position) Move(move move.Move) Position {
 	return From(p.row+move.NumberOfRows(), p.column+move.NumberOfColumns())
 }
+
+func (p position) String() string {
+	return fmt.Sprintf("c: %d r: %d", p.column, p.row)
+}