diff --git a/c/2024/12/garden_groups.c b/c/2024/12/garden_groups.c
new file mode 100644
index 0000000..7a08287
--- /dev/null
+++ b/c/2024/12/garden_groups.c
@@ -0,0 +1,135 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdbool.h>
+
+#include "../../lib/aoc.h"
+
+struct Map;
+
+typedef struct Region {
+  struct Map *map;
+  char plant;
+  int positions[1000];
+  int positions_count;
+} Region;
+
+typedef struct Map {
+  char *data;
+  int width;
+  int height;
+  int input_length;
+  Region regions[1000];
+  int regions_count;
+} Map;
+
+int region_perimeter(Region *r) {
+  int perimeter = 0;
+  for (int i = 0; i < r->positions_count; i++) {
+    int position = r->positions[i];
+    if (position - r->map->width < 0 || r->map->data[position - r->map->width] != r->plant - 'A' + 'a') {
+      perimeter++;
+    }
+
+    if (position - 1 < 0 || r->map->data[position - 1] != r->plant - 'A' + 'a') {
+      perimeter++;
+    }
+
+    if (position + 1 > r->map->input_length || r->map->data[position + 1] != r->plant - 'A' + 'a') {
+      perimeter++;
+    }
+    if (position + r->map->width > r->map->input_length || r->map->data[position + r->map->width] != r->plant - 'A' + 'a') {
+      perimeter++;
+    }
+  }
+  return perimeter;
+}
+
+int region_price(Region *r) {
+  int rp = region_perimeter(r);
+  int price = rp * r->positions_count;
+  return price;
+}
+
+int main() {
+  char *input = aoc_read_input();
+  int input_length = strlen(input);
+
+  Map m;
+  fflush(stdout);
+  m.data = input;
+  m.width = strchr(input, '\n') - input + 1;
+  m.height = input_length / m.width;
+  m.regions_count = 0;
+  m.input_length = input_length;
+
+  // initialize regions
+  for (int i = 0; i < input_length; i++) {
+    if (m.data[i] == '\n' || m.data[i] < 'A' || m.data[i] > 'Z') continue;
+
+    Region *r = &(m.regions[m.regions_count++]);
+    r->plant = m.data[i];
+    r->positions_count = 0;
+    r->map = &m;
+
+    int next_positions[1000];
+    next_positions[0] = i;
+    int next_positions_count = 1;
+
+    int nn_positions[1000];
+    int nn_positions_count = 0;
+
+    while (next_positions_count > 0) {
+      for (int j = 0; j < next_positions_count; j++) {
+	int next_position = next_positions[j];
+	r->positions[r->positions_count++] = next_position;
+	m.data[next_position] = m.data[next_position] - 'A' + 'a';
+      }
+
+      for (int j = 0; j < next_positions_count; j++) {
+	int next_position = next_positions[j];
+	if (next_position - m.width > 0 && m.data[next_position - m.width] == r->plant) {
+	  nn_positions[nn_positions_count++] = next_position - m.width;
+	}
+
+	if (next_position - 1 > 0 && m.data[next_position - 1] == r->plant) {
+	  nn_positions[nn_positions_count++] = next_position - 1;
+	}
+
+	if (next_position + 1 < input_length && m.data[next_position + 1] == r->plant) {
+	  nn_positions[nn_positions_count++] = next_position + 1;
+	}
+
+	if (next_position + m.width < input_length && m.data[next_position + m.width] == r->plant) {
+	  nn_positions[nn_positions_count++] = next_position + m.width;
+	}
+      }
+
+      qsort(nn_positions, nn_positions_count, sizeof(int), aoc_sort_int);
+      if (nn_positions_count == 0) break;
+
+      next_positions_count = 1;
+      next_positions[0] = nn_positions[0];
+      for (int j = 1; j < nn_positions_count; j++) {
+	if (nn_positions[j] != next_positions[next_positions_count - 1]) {
+	  next_positions[next_positions_count++] = nn_positions[j];
+	}
+      }
+
+      nn_positions_count = 0;
+    }
+  }
+
+  int cost = 0;
+
+  for (int i = 0; i < m.regions_count; i++) {
+    cost += region_price(&m.regions[i]);
+    // printf("%c: %d\n", m.regions[i].plant, m.regions[i].positions_count);
+  }
+
+  printf("Part 1: %d\n", cost);
+  // printf("Part 2: %lld\n", big_stone_count_sum);
+  
+  aoc_free();
+  return 0;
+}