diff --git a/src/day12.rs b/src/day12.rs
new file mode 100644
index 0000000..568ad06
--- /dev/null
+++ b/src/day12.rs
@@ -0,0 +1,70 @@
+use std::{collections::HashSet, fs::read_to_string};
+
+use crate::utils::grid::{Coord, Grid};
+
+pub fn day_main() {
+    let input = read_to_string("input/day12.txt").unwrap();
+    let input = input.trim();
+    println!(" part1: {}", part1(input));
+    println!(" part2: {}", part2(input));
+}
+
+type RiddleResult = u64;
+
+const NEIGHBORS: &[Coord] = &[(1, 0), (0, 1), (-1, 0), (0, -1)];
+
+fn part1(input: &str) -> RiddleResult {
+    let garden = Grid::parse(input);
+    let mut processed: HashSet<Coord> = HashSet::new();
+    let mut result = 0;
+    for (p, c) in garden.entries() {
+        if processed.contains(&p) {
+            continue;
+        }
+        let mut area = 0;
+        let mut fence = 0;
+        let mut further = vec![p];
+        while let Some(current) = further.pop() {
+            if processed.contains(&current) {
+                continue;
+            }
+            area += 1;
+            for next in NEIGHBORS.iter().map(|d| (current.0 + d.0, current.1 + d.1)) {
+                let next_c = garden.get(next);
+                if next_c.is_none() || next_c.unwrap() != c {
+                    fence += 1;
+                } else {
+                    further.push(next);
+                }
+            }
+            processed.insert(current);
+        }
+        result += area * fence;
+    }
+    result
+}
+
+fn part2(_input: &str) -> RiddleResult {
+    0
+}
+
+#[cfg(test)]
+mod test {
+    use super::{part1, part2};
+
+    const TEST_INPUT: &str = r"AAAA
+BBCD
+BBCC
+EEEC
+";
+
+    #[test]
+    fn test1() {
+        assert_eq!(part1(TEST_INPUT), 140);
+    }
+
+    #[test]
+    fn test2() {
+        assert_eq!(part2(TEST_INPUT), 0);
+    }
+}
diff --git a/src/lib.rs b/src/lib.rs
index cb167e1..1fd7d50 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -9,5 +9,6 @@ pub mod day08;
 pub mod day09;
 pub mod day10;
 pub mod day11;
+pub mod day12;
 // PLACEHOLDER
 pub mod utils;
diff --git a/src/main.rs b/src/main.rs
index 6a4cda3..71345d0 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -16,6 +16,7 @@ fn main() {
         (9, day09::day_main),
         (10, day10::day_main),
         (11, day11::day_main),
+        (12, day12::day_main),
         // PLACEHOLDER
     ]);
     let day: Option<u8> = args().nth(1).and_then(|a| a.parse().ok());