feat: solve part one using prebuilt map for rolls

internal/2025/DayFour/code.go

@@ -0,0 +1,65 @@
+package dayfour
+
+import (
+	"os"
+	"strings"
+
+	"advent-of-code/internal/registry"
+)
+
+type position struct {
+	row, column int
+}
+
+func init() {
+	registry.Register("2025D4", ParseInput, PartOne, PartTwo)
+}
+
+func ParseInput(filepath string) []string {
+	content, _ := os.ReadFile(filepath)
+	return strings.Split(string(content), "\n")
+}
+
+func PartOne(data []string) int {
+	rollPositions := make(map[position]bool)
+
+	for row := range data {
+		for column := 0; column < len(data[row]); column++ {
+			if data[row][column] == '@' {
+				rollPositions[position{row, column}] = true
+			}
+		}
+	}
+
+	accessibleRolls := 0
+	directions := []position{
+		{-1, -1},
+		{-1, 0},
+		{-1, 1},
+		{0, -1},
+		{0, 1},
+		{1, -1},
+		{1, 0},
+		{1, 1},
+	}
+
+	for pos := range rollPositions {
+		adjacentRolls := 0
+		for _, direction := range directions {
+			neighbor := position{pos.row + direction.row, pos.column + direction.column}
+			if rollPositions[neighbor] {
+				adjacentRolls++
+			}
+		}
+
+		if adjacentRolls < 4 {
+			accessibleRolls++
+		}
+	}
+
+	return accessibleRolls
+}
+
+func PartTwo(data []string) int {
+	return 0
+}