diff --git a/data/examples/20.txt b/data/examples/20.txt
new file mode 100644
index 000000000..c097dae
--- /dev/null
+++ b/data/examples/20.txt
@@ -0,0 +1,15 @@
+###############
+#...#...#.....#
+#.#.#.#.#.###.#
+#S#...#.#.#...#
+#######.#.#.###
+#######.#.#...#
+#######.#.###.#
+###..E#...#...#
+###.#######.###
+#...###...#...#
+#.#####.#.###.#
+#.#...#.#.#...#
+#.#.#.#.#.#.###
+#...#...#...###
+###############
diff --git a/data/examples/21.txt b/data/examples/21.txt
new file mode 100644
index 000000000..4cf0c29
--- /dev/null
+++ b/data/examples/21.txt
@@ -0,0 +1,5 @@
+029A
+980A
+179A
+456A
+379A
diff --git a/src/bin/20.rs b/src/bin/20.rs
new file mode 100644
index 000000000..621a0df
--- /dev/null
+++ b/src/bin/20.rs
@@ -0,0 +1,148 @@
+use std::collections::VecDeque;
+
+use aoc::grid_vec::{Direction, Grid, Point};
+use hashbrown::HashMap;
+
+fn parse_input(input: &str) -> (Grid, Point, Point) {
+    let mut grid: Grid = input.parse().unwrap();
+    let start = grid.find(b'S').unwrap();
+    let end = grid.find(b'E').unwrap();
+
+    grid[start] = b'.';
+    grid[end] = b'.';
+
+    (grid, start, end)
+}
+fn bfs(
+    grid: &Grid,
+    start: Point,
+    limit: Option<usize>,
+    cheat: bool,
+    visited: &mut HashMap<Point, usize>,
+    queue: &mut VecDeque<(Point, usize)>,
+) {
+    visited.clear();
+    queue.clear();
+
+    queue.push_back((start, 0));
+
+    while let Some((p, l)) = queue.pop_front() {
+        if visited.contains_key(&p) {
+            continue;
+        }
+        visited.insert(p, l);
+
+        for d in Direction::CROSS {
+            let n = p + d;
+
+            let nv = grid.get(&n);
+            let uwnv = *nv.unwrap_or(&b'#');
+            let valid_neigh = (cheat && nv.is_some()) || uwnv == b'.';
+            let valid_length = l < limit.unwrap_or(usize::MAX);
+            let unvisited = !visited.contains_key(&n);
+
+            if valid_neigh && valid_length && unvisited {
+                queue.push_back((n, l + 1));
+            }
+        }
+    }
+}
+
+fn get_cheat_neighbours_and_benchmark(
+    grid: &Grid,
+    start: Point,
+    cheat_limit: usize,
+) -> HashMap<Point, Vec<(Point, usize)>> {
+    let mut map = HashMap::<Point, Vec<(Point, usize)>>::new();
+
+    let mut reuse_queue = VecDeque::new();
+    let mut reuse_visited = HashMap::new();
+
+    let mut valid_points = HashMap::new();
+
+    bfs(
+        grid,
+        start,
+        None,
+        false,
+        &mut valid_points,
+        &mut reuse_queue,
+    );
+
+    for (&s, _) in valid_points.iter() {
+        bfs(
+            grid,
+            s,
+            Some(cheat_limit),
+            true,
+            &mut reuse_visited,
+            &mut reuse_queue,
+        );
+        for (&point, &length) in reuse_visited.iter().filter(|(&p, _)| grid[p] == b'.') {
+            map.entry(s).or_default().push((point, length));
+        }
+    }
+
+    map
+}
+
+fn cheated_bfs(
+    grid: &Grid,
+    start: Point,
+    end: Point,
+    cheat_limit: usize,
+    increase_limit: usize,
+) -> usize {
+    let neighbours = get_cheat_neighbours_and_benchmark(grid, start, cheat_limit);
+
+    let mut reuse_queue = VecDeque::new();
+
+    let mut from_start = HashMap::new();
+    let mut from_end = HashMap::new();
+
+    bfs(grid, start, None, false, &mut from_start, &mut reuse_queue);
+    bfs(grid, end, None, false, &mut from_end, &mut reuse_queue);
+
+    let benchmark = from_start[&end];
+
+    let mut count = 0;
+
+    for node in from_start.keys() {
+        for (neigh, cheat_dist) in neighbours[node].iter() {
+            let start_dist = from_start[node];
+            let end_dist = from_end[neigh];
+
+            let dist = start_dist + cheat_dist + end_dist;
+            if dist < benchmark && dist.abs_diff(benchmark) >= increase_limit {
+                count += 1;
+            }
+        }
+    }
+
+    count
+}
+
+pub fn part_one(input: &str) -> Option<usize> {
+    let (grid, start, end) = parse_input(input);
+    cheated_bfs(&grid, start, end, 2, 100).into()
+}
+
+pub fn part_two(input: &str) -> Option<usize> {
+    let (grid, start, end) = parse_input(input);
+    cheated_bfs(&grid, start, end, 20, 100).into()
+}
+
+aoc::solution!(20);
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    #[test]
+    fn test_part_one() {
+        assert_eq!(part_one(&aoc::template::read_file("examples", 20)), None);
+    }
+    #[test]
+    fn test_part_two() {
+        assert_eq!(part_two(&aoc::template::read_file("examples", 20)), None);
+    }
+}
diff --git a/src/bin/21.rs b/src/bin/21.rs
new file mode 100644
index 000000000..915cd24
--- /dev/null
+++ b/src/bin/21.rs
@@ -0,0 +1,262 @@
+use std::iter::once;
+
+use hashbrown::{HashMap, HashSet};
+use itertools::Itertools;
+
+const NUMPAD: [(&str, &str); 110] = [
+    // 0 - everywhere
+    ("01", "^<"),
+    ("02", "^"),
+    ("03", "^>"),
+    ("04", "^^<"),
+    ("05", "^^"),
+    ("06", "^^>"),
+    ("07", "^^^<"),
+    ("08", "^^^"),
+    ("09", "^^^>"),
+    ("0A", ">"),
+    // 1 - everywhere
+    ("10", ">v"),
+    ("12", ">"),
+    ("13", ">>"),
+    ("14", "^"),
+    ("15", "^>"),
+    ("16", "^>>"),
+    ("17", "^^"),
+    ("18", "^^>"),
+    ("19", "^^>>"),
+    ("1A", ">>v"),
+    // 2 - everywhere
+    ("20", "v"),
+    ("21", "<"),
+    ("23", ">"),
+    ("24", "^<"),
+    ("25", "^"),
+    ("26", "^>"),
+    ("27", "^^<"),
+    ("28", "^^"),
+    ("29", "^^>"),
+    ("2A", ">v"),
+    // 3 - everywhere
+    ("30", "v<"),
+    ("31", "<<"),
+    ("32", "<"),
+    ("34", "^<<"),
+    ("35", "^<"),
+    ("36", "^"),
+    ("37", "^^<<"),
+    ("38", "^^<"),
+    ("39", "^^"),
+    ("3A", "v"),
+    // 4 - everywhere
+    ("40", ">vv"),
+    ("41", "v"),
+    ("42", "v>"),
+    ("43", "v>>"),
+    ("45", ">"),
+    ("46", ">>"),
+    ("47", "^"),
+    ("48", "^>"),
+    ("49", "^>>"),
+    ("4A", ">>vv"),
+    // 5 - everywhere
+    ("50", "vv"),
+    ("51", "v<"),
+    ("52", "v"),
+    ("53", "v>"),
+    ("54", "<"),
+    ("56", ">"),
+    ("57", "^<"),
+    ("58", "^"),
+    ("59", "^>"),
+    ("5A", ">vv"),
+    // 6 - everywhere
+    ("60", "vv<"),
+    ("61", "v<<"),
+    ("62", "v<"),
+    ("63", "v"),
+    ("64", "<<"),
+    ("65", "<"),
+    ("67", "^<<"),
+    ("68", "^<"),
+    ("69", "^"),
+    ("6A", "vv"),
+    // 7 - everywhere
+    ("70", ">vvv"),
+    ("71", "vv"),
+    ("72", "vv>"),
+    ("73", "vv>>"),
+    ("74", "v"),
+    ("75", "v>"),
+    ("76", "v>>"),
+    ("78", ">"),
+    ("79", ">>"),
+    ("7A", ">>vvv"),
+    // 8 - everywhere
+    ("80", "vvv"),
+    ("81", "vv<"),
+    ("82", "vv"),
+    ("83", "vv>"),
+    ("84", "v<"),
+    ("85", "v"),
+    ("86", "v>"),
+    ("87", "<"),
+    ("89", ">"),
+    ("8A", ">vvv"),
+    // 9 - everywhere
+    ("90", "<vvv"),
+    ("91", "vv<<"),
+    ("92", "vv<"),
+    ("93", "vv"),
+    ("94", "v<<"),
+    ("95", "v<"),
+    ("96", "v"),
+    ("97", "<<"),
+    ("98", "<"),
+    ("9A", "vvv"),
+    // A - everywhere
+    ("A0", "<"),
+    ("A1", "^<<"),
+    ("A2", "^<"),
+    ("A3", "^"),
+    ("A4", "^^<<"),
+    ("A5", "^^<"),
+    ("A6", "^^"),
+    ("A7", "^^^<<"),
+    ("A8", "^^^<"),
+    ("A9", "^^^"),
+];
+
+const KEYPAD: [(&str, &str); 20] = [
+    // < - everywhere
+    ("<v", ">"),
+    ("<>", ">>"),
+    ("<^", ">^"),
+    ("<A", ">>^"),
+    // v - everywhere
+    ("v<", "<"),
+    ("v>", ">"),
+    ("v^", "^"),
+    ("vA", ">^"),
+    // > - everywhere
+    ("><", "<<"),
+    (">v", "<"),
+    (">^", "^<"),
+    (">A", "^"),
+    // ^ - everywhere
+    ("^<", "v<"),
+    ("^v", "v"),
+    ("^>", "v>"),
+    ("^A", ">"),
+    // A - everywhere
+    ("A<", "v<<"),
+    ("Av", "v<"),
+    ("A>", "v"),
+    ("A^", "<"),
+];
+
+fn build_move_options(s: &str) -> Vec<String> {
+    let mut set = HashSet::new();
+
+    for c in s.chars() {
+        set.insert(c);
+    }
+
+    let mut v = vec![s.to_string()];
+
+    if set.len() == 2 {
+        v.push(s.chars().rev().collect())
+    }
+
+    v
+}
+
+pub fn part_one(input: &str) -> Option<usize> {
+    let mut keypad = HashMap::new();
+
+    for (k, v) in KEYPAD.iter() {
+        let key = k.as_bytes();
+        keypad.insert((key[0], key[1]), build_move_options(v));
+    }
+
+    let mut numpad = HashMap::new();
+
+    for (k, v) in NUMPAD.iter() {
+        let key = k.as_bytes();
+        numpad.insert((key[0], key[1]), build_move_options(v));
+    }
+
+    let mut s1s = Vec::new();
+    let mut s2s = Vec::new();
+    let mut s3s = Vec::new();
+    let mut s4s = Vec::new();
+
+    let mut c = 0;
+
+    for line in input.lines() {
+        s1s.clear();
+        s2s.clear();
+        s3s.clear();
+        s4s.clear();
+
+        s1s.push(once(&b'A').chain(line.as_bytes()).copied().collect_vec());
+
+        for mapper in [&numpad, &keypad, &keypad] {
+            for s1 in s1s.iter() {
+                s3s.push(vec![b'A']);
+                for i in 1..s1.len() {
+                    let k2 = s1[i - 1];
+                    let k1 = s1[i];
+
+                    if mapper.contains_key(&(k1, k2)) {
+                        for path in mapper[&(k1, k2)].iter() {
+                            for s3 in s3s.iter() {
+                                let mut cs3 = s3.clone();
+                                cs3.extend(path.as_bytes());
+                                s4s.push(cs3);
+                            }
+                        }
+                    }
+
+                    s3s.clear();
+                    s3s.append(&mut s4s);
+
+                    for s3 in s3s.iter_mut() {
+                        s3.push(b'A');
+                    }
+                }
+                s2s.append(&mut s3s);
+            }
+
+            s1s.clear();
+            s1s.append(&mut s2s);
+        }
+
+        let min_len = s1s.iter().map(|v| v.len()).min().unwrap();
+        let n: usize = line.strip_suffix("A").unwrap().parse().unwrap();
+
+        println!("{min_len}, {n}");
+        c += n * min_len;
+    }
+
+    c.into()
+}
+
+pub fn part_two(input: &str) -> Option<usize> {
+    None
+}
+
+aoc::solution!(21);
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    #[test]
+    fn test_part_one() {
+        assert_eq!(part_one(&aoc::template::read_file("examples", 21)), None);
+    }
+    #[test]
+    fn test_part_two() {
+        assert_eq!(part_two(&aoc::template::read_file("examples", 21)), None);
+    }
+}