diff --git a/lib/day12.dart b/lib/day12.dart
index 3783c73..9db58d3 100644
--- a/lib/day12.dart
+++ b/lib/day12.dart
@@ -1,6 +1,125 @@
 // --- Day 12: Garden Groups ---
 // https://adventofcode.com/2024/day/12
 
-int solveA(Iterable<String> input) {
-  return 0;
+import 'dart:collection';
+import 'dart:typed_data';
+
+int solveA(List<String> input) {
+  final grid = Grid(input);
+
+  Queue<Point> todo = Queue()..add(Point(0, 0));
+  Set<Point> pointsAlreadyPartOfGroup = HashSet();
+  List<List<Point>> groups = [];
+
+  while (todo.isNotEmpty) {
+    final currentPoint = todo.removeFirst();
+
+    if (pointsAlreadyPartOfGroup.contains(currentPoint)) {
+      continue;
+    }
+
+    final result =
+        scan(currentPoint, grid.getByPoint(currentPoint), grid, todo, {})
+            .toList();
+    groups.add(result);
+
+    pointsAlreadyPartOfGroup.addAll(result);
+  }
+
+  var sum = 0;
+  for (final group in groups) {
+    var fences = 0;
+
+    for (final point in group) {
+      final currentChar = grid.getByPoint(point);
+
+      for (final scan in scanningList) {
+        if (grid.getByPoint(point + scan) != currentChar) {
+          fences++;
+        }
+      }
+    }
+
+    sum += (fences * group.length);
+  }
+
+  return sum;
+}
+
+List<Point> scanningList = const [
+  Point(0, -1), // up
+  Point(1, 0), // right
+  Point(0, 1), // down
+  Point(-1, 0), // left
+];
+
+Iterable<Point> scan(
+  Point currentPoint,
+  int lookFor,
+  Grid grid,
+  Queue<Point> todo,
+  Set<Point> history,
+) sync* {
+  if (!history.add(currentPoint)) {
+    return;
+  }
+
+  final currentValue = grid.getByPoint(currentPoint);
+
+  if (currentValue == 0) {
+    return;
+  }
+
+  if (currentValue != lookFor) {
+    todo.add(currentPoint);
+    return;
+  }
+
+  yield currentPoint;
+
+  for (final scanning in scanningList) {
+    yield* scan(currentPoint + scanning, lookFor, grid, todo, history);
+  }
+}
+
+extension type const Point._(({int x, int y}) _point) {
+  const Point(int x, int y) : this._((x: x, y: y));
+
+  int get x => _point.x;
+  int get y => _point.y;
+
+  Point operator +(Point other) => Point(
+        x + other.x,
+        y + other.y,
+      );
+
+  Point operator -(Point other) => Point(
+        x - other.x,
+        y - other.y,
+      );
+}
+
+class Grid {
+  final int length, height;
+  final Uint8List _list;
+
+  Grid(List<String> input)
+      : length = input.first.length,
+        height = input.length,
+        _list = Uint8List((input.length * input.first.length)) {
+    for (final (y, line) in input.indexed) {
+      for (var x = 0; x < line.length; x++) {
+        set(x, y, line.codeUnitAt(x));
+      }
+    }
+  }
+
+  int getByPoint(Point p) => get(p.x, p.y);
+  int get(int x, int y) =>
+      (x < 0 || y < 0 || x >= length || y >= height) ? 0 : _list[_getPos(x, y)];
+
+  void setByPoint(Point p, int value) => set(p.x, p.y, value);
+  void set(int x, int y, int value) => _list[_getPos(x, y)] = value;
+
+  int _getPos(int x, int y) => x + (y * length);
 }
diff --git a/test/day12_test.dart b/test/day12_test.dart
index 740051f..558080a 100644
--- a/test/day12_test.dart
+++ b/test/day12_test.dart
@@ -18,7 +18,7 @@ BBCD
 BBCC
 EEEC
 '''
-              .asLines),
+              .toLinesList()),
           equals(140));
     });
     test('Example 2', () {
@@ -30,7 +30,7 @@ OOOOO
 OXOXO
 OOOOO
 '''
-              .asLines),
+              .toLinesList()),
           equals(772));
     });
     test('Example 3', () {
@@ -47,11 +47,11 @@ MIIIIIJJEE
 MIIISIJEEE
 MMMISSJEEE
 '''
-              .asLines),
+              .toLinesList()),
           equals(1930));
     });
     test('Solution', () {
-      expect(solveA(input), equals(-1));
+      expect(solveA(input), equals(1387004));
     });
-  }, skip: true);
+  });
 }