diff --git a/samples/day12.txt b/samples/day12.txt
new file mode 100644
index 0000000..e925935
--- /dev/null
+++ b/samples/day12.txt
@@ -0,0 +1,6 @@
+???.### 1,1,3
+.??..??...?##. 1,1,3
+?#?#?#?#?#?#?#? 1,3,1,6
+????.#...#... 4,1,1
+????.######..#####. 1,6,5
+?###???????? 3,2,1
diff --git a/src/bin/day12.rs b/src/bin/day12.rs
new file mode 100644
index 0000000..bb3affd
--- /dev/null
+++ b/src/bin/day12.rs
@@ -0,0 +1,230 @@
+use std::{collections::VecDeque, str::FromStr};
+
+use indicatif::ParallelProgressIterator;
+use memoize::memoize;
+use rayon::prelude::*;
+
+use aoc_2023::*;
+
+type Output1 = usize;
+type Output2 = Output1;
+
+#[derive(Debug)]
+struct Row {
+    map: VecDeque<char>,
+    damaged: VecDeque<usize>,
+    // cache: HashMap<(usize, usize, bool), usize>,
+}
+
+impl FromStr for Row {
+    type Err = &'static str;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        let (map, damaged) = s.split_once(' ').unwrap();
+
+        let map = map.chars().collect();
+        let damaged = parse_separated(',', damaged);
+
+        Ok(Row::new(map, damaged))
+    }
+}
+
+#[memoize]
+fn arrangements(
+    mut map: VecDeque<char>,
+    mut damaged: VecDeque<usize>,
+    mut in_damaged: bool,
+) -> usize {
+    // all damaged have been placed
+    if damaged.is_empty() {
+        return if map.iter().all(|&c| c == '.' || c == '?') {
+            1
+        } else {
+            0
+        };
+    }
+
+    // skip the functional
+    while let Some('.') = map.front() {
+        if in_damaged {
+            return 0;
+        }
+
+        in_damaged = false;
+        map.pop_front();
+    }
+
+    if map.is_empty() || damaged.is_empty() {
+        return 0;
+    }
+
+    match map[0] {
+        '?' => {
+            map[0] = '#';
+            let as_non_functional = arrangements(map.clone(), damaged.clone(), true);
+
+            map[0] = '.';
+            let as_functional = if !in_damaged {
+                arrangements(map, damaged, false)
+            } else {
+                0
+            };
+
+            as_functional + as_non_functional
+        }
+        '#' if damaged.is_empty() => 0,
+        '#' => {
+            damaged[0] -= 1;
+
+            if damaged[0] == 0 {
+                if 1 < map.len() && map[1] == '#' {
+                    0
+                } else if 1 < map.len() {
+                    map[1] = '.';
+                    arrangements(
+                        map.iter().cloned().skip(1).collect(),
+                        damaged.iter().cloned().skip(1).collect(),
+                        false,
+                    )
+                } else {
+                    let result = arrangements(
+                        map.iter().cloned().skip(2).collect(),
+                        damaged.iter().cloned().skip(1).collect(),
+                        false,
+                    );
+                    result
+                }
+            } else {
+                let result = arrangements(map.iter().cloned().skip(1).collect(), damaged, true);
+                result
+            }
+        }
+        _ => unreachable!(),
+    }
+}
+
+impl Row {
+    fn new(map: Vec<char>, damaged: Vec<usize>) -> Row {
+        Row {
+            map: VecDeque::from(map),
+            damaged: VecDeque::from(damaged),
+            // cache: HashMap::new(),
+        }
+    }
+
+    fn arrangements(&mut self) -> usize {
+        arrangements(self.map.clone(), self.damaged.clone(), false)
+    }
+
+    fn unfold(&self) -> Row {
+        Row::new(
+            vec![self.map.iter().collect::<String>(); 5]
+                .join("?")
+                .chars()
+                .collect_vec(),
+            self.damaged
+                .iter()
+                .cloned()
+                .cycle()
+                .take(5 * self.damaged.len())
+                .collect_vec(),
+        )
+    }
+}
+
+struct Day12 {
+    rows: Vec<Row>,
+}
+impl Solution<Output1, Output2> for Day12 {
+    fn new<P: AsRef<Path>>(pathname: P) -> Self {
+        Self {
+            rows: file_to_structs(pathname),
+        }
+    }
+
+    fn part_1(&mut self) -> Output1 {
+        self.rows.iter_mut().map(|r| r.arrangements()).sum()
+    }
+
+    fn part_2(&mut self) -> Output2 {
+        self.rows
+            .par_iter()
+            .progress()
+            .map(|r| r.unfold().arrangements())
+            .sum()
+    }
+}
+
+fn main() -> Result<()> {
+    // Day12::run("sample")
+    Day12::main()
+}
+
+test_sample!(day_12, Day12, 21, 525152);
+
+#[cfg(test)]
+mod day_12_extended {
+    use super::*;
+
+    #[test]
+    fn arrangements_1() {
+        let mut row = Row::new("???.###".chars().collect_vec(), vec![1, 1, 3]);
+
+        assert_eq!(row.arrangements(), 1);
+        assert_eq!(row.unfold().arrangements(), 1);
+    }
+
+    #[test]
+    fn arrangements_2() {
+        let mut row = Row::new(".??..??...?##.".chars().collect_vec(), vec![1, 1, 3]);
+
+        assert_eq!(row.arrangements(), 4);
+        assert_eq!(row.unfold().arrangements(), 16384);
+    }
+
+    #[test]
+    fn arrangements_3() {
+        let mut row = Row::new("?#?#?#?#?#?#?#?".chars().collect_vec(), vec![1, 3, 1, 6]);
+
+        assert_eq!(row.arrangements(), 1);
+        assert_eq!(row.unfold().arrangements(), 1);
+    }
+
+    #[test]
+    fn arrangements_4() {
+        let mut row = Row::new("????.#...#...".chars().collect_vec(), vec![4, 1, 1]);
+
+        assert_eq!(row.arrangements(), 1);
+        assert_eq!(row.unfold().arrangements(), 16);
+    }
+
+    #[test]
+    fn arrangements_5() {
+        let mut row = Row::new("????.######..#####.".chars().collect_vec(), vec![1, 6, 5]);
+
+        assert_eq!(row.arrangements(), 4);
+        assert_eq!(row.unfold().arrangements(), 2500);
+    }
+
+    #[test]
+    fn arrangements_6() {
+        let mut row = Row::new("?###????????".chars().collect_vec(), vec![3, 2, 1]);
+
+        assert_eq!(row.arrangements(), 10);
+        assert_eq!(row.unfold().arrangements(), 506250);
+    }
+
+    #[test]
+    fn arrangements_7() {
+        let mut row = Row::new("????????????".chars().collect_vec(), vec![3, 2, 1]);
+
+        assert_eq!(row.arrangements(), 35);
+    }
+
+    #[test]
+    fn arrangements_8() {
+        let mut row = Row::new("???#?#?????.?##??#".chars().collect_vec(), vec![8, 6]);
+
+        assert_eq!(row.arrangements(), 4);
+    }
+}