feat: solve part two with iterative process

internal/2025/DayFour/code.go

@@ -11,6 +11,17 @@ type position struct {
 	row, column int
 }
 
+var directions = []position{
+	{-1, -1},
+	{-1, 0},
+	{-1, 1},
+	{0, -1},
+	{0, 1},
+	{1, -1},
+	{1, 0},
+	{1, 1},
+}
+
 func init() {
 	registry.Register("2025D4", ParseInput, PartOne, PartTwo)
 }
@@ -32,17 +43,6 @@ func PartOne(data []string) int {
 	}
 
 	accessibleRolls := 0
-	directions := []position{
-		{-1, -1},
-		{-1, 0},
-		{-1, 1},
-		{0, -1},
-		{0, 1},
-		{1, -1},
-		{1, 0},
-		{1, 1},
-	}
-
 	for pos := range isRoll {
 		adjacentRolls := 0
 		for _, direction := range directions {
@@ -61,5 +61,44 @@ func PartOne(data []string) int {
 }
 
 func PartTwo(data []string) int {
-	return 0
+	isRoll := make(map[position]bool)
+
+	for row := range data {
+		for column := 0; column < len(data[row]); column++ {
+			if data[row][column] == '@' {
+				isRoll[position{row, column}] = true
+			}
+		}
+	}
+
+	totalRemoved := 0
+
+	for {
+		accessibleRolls := make(map[position]bool)
+
+		for pos := range isRoll {
+			adjacentRolls := 0
+			for _, direction := range directions {
+				neighbor := position{pos.row + direction.row, pos.column + direction.column}
+				if isRoll[neighbor] {
+					adjacentRolls++
+				}
+			}
+
+			if adjacentRolls < 4 {
+				accessibleRolls[pos] = true
+			}
+		}
+
+		if len(accessibleRolls) == 0 {
+			break
+		}
+
+		for pos := range accessibleRolls {
+			delete(isRoll, pos)
+			totalRemoved++
+		}
+	}
+
+	return totalRemoved
 }