diff --git a/day12/Cargo.lock b/day12/Cargo.lock
new file mode 100644
index 0000000..5e9bbe3
--- /dev/null
+++ b/day12/Cargo.lock
@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "day12"
+version = "0.1.0"
diff --git a/day12/input.txt b/day12/input.txt
new file mode 100644
index 0000000..4ff75ee
--- /dev/null
+++ b/day12/input.txt
@@ -0,0 +1,41 @@
+abcccccccccccccccccccccccccccccccccccccaaaaaaacccccccaaaaaaaaaaaccccccccccccccccccccaaacaaaaaaaacccccccccccccccccccccccccccccccccccaaaaa
+abccccccccccccccccccaaccaacccccccccccccaaaaaaaccccccccaaaaaaaaaaacccccccaaaaccccccccaaaaaaaaaaaaacccccccccccccccccccccccccccccccccaaaaaa
+abccccccccccccccccccaaaaaaccccccccccaaaccaaaaaacccccccaaaaaaaaaaccccccccaaaaccccccaaaaaaaaaaaaaaacccccccccccccccccccaaacccccccccccaaaaaa
+abcccccccccccccccccccaaaaacccccccccccaaccaacaaaccccccaaaaaaaaaaaccccccccaaaacccccaaaaaaaaacaaaaaaacccccccccccccccccaaaacccccccccccaaacaa
+abccccccccccccccccccaaaaaaccccccccaacaaaaaacccccccccaaaaaaaaaaaaacaaaccccaaccccccaaaaaaaaacaacccccccccccccccccaaaccaaaacccccccccccccccaa
+abcccccccccccccccccaaaaaaaacccccccaaaaaaaaccccccaaaaaaaacaaaacaaaaaaacccccccccaaccccaaaaaacaaacccccccccccccccaaaakkkaaccccccccccccccccaa
+abcccccccccccccccccaaaaaaaaccccccccaaaaaccccaacccaaaaaaaaaaaacaaaaaaccccccccccaacccaaaaaaaaaaaacccccccccccccccakkkkkklcccccccccccccccccc
+abaaacccccccccccaaccccaaccccccccccccaaaaaccaaacccaaaaaaaaaaaaaaaaaaaaccccccaaaaaaaacaacccaaaaaaccccccccccccccckkkkkkkllcccccccaaaccccccc
+abaaaacccccccaacaaccccaacccccccccccaaacaaaaaaaccccaaaaaaaaaaaaaaaaaaaacccccaaaaaaaaaaaccccaaaaacccccccccccccckkkksssllllccccccaaaaaacccc
+abaaaacccccccaaaaacccccccccccaaaccccaacaaaaaaccccaaaaaacaaaaaaaaaaaaaacccccccaaaaccccccccaaaaacccccccccccccckkkksssssllllcccccaaaaaacccc
+abaaacccccccccaaaaaaccccccccaaaaccccccccaaaaaaaacaaaaaaaaaaaaacaaacaaacccccccaaaaacccccccaaaaacccccccccccccjkkkrssssssllllccccccaaaccccc
+abccccccccccaaaaaaaaccccccccaaaacccccccaaaaaaaaacaacaaaaaaaaaacaaaccccccccccaaacaaccccccccccccccccccccccccjjkkrrsuuussslllllcccccaaccccc
+abccaaacccccaaaaacccccccccccaaaaccccccaaaaaaaaaacccccaaaaaaaaaacaaccccccccccaacccacccccccccccccccccccccjjjjjjrrrsuuuussslllllmcccddacccc
+abcccaaaccaccacaaaccccccccccccccccccccaaaaaaaccccccccccaaaaaaaaccccccaacccccccccccaaaaacccccccccccccccjjjjjjrrrruuuuuusssllmmmmmddddcccc
+abccaaaaaaaacccaaaccccccccccccccccaaacccccaaaccccccccccccaaacccccccccaacccccccccccaaaaacccccccccccccjjjjjrrrrrruuuxuuussqqqqmmmmmdddcccc
+abcaaaaaaaacccaaaaaacaaaaaccccccaaaaaaccccaaacccaaccccccccaaccccccaaaaaaaaccaaacccaaaaaaccccccccccccjjjjrrrrrruuuxxxuuuqqqqqqqmmmdddcccc
+abaaaaaaaaaccccaaaaacaaaaaccccccaaaaaaaaccccccaaaaaaccccccccccccccaaaaaaaaccaaacaaaaaaaacccccccccccjjjjrrrtttuuuuxxxyvvvvvqqqqmmmdddcccc
+abaaaaaaaaaccaaaaaaacaaaaaaccccccaaaaaaaacccccaaaaaaccccccccccccccccaaaaccaaaaaaaaaaaaaacccccccccaaiijqqqrttttuuuxxyyvvvvvvvqqmmmdddcccc
+abcaaaaaaaaccaaaaaaaaaaaaaacccccaaaaaaaacccccccaaaacccccaaaaccccccccaaaaacaaaaaaaaccaaccccccccccaaaiiiqqqttttxxxxxxyyyyyyvvvqqmmmdddcccc
+abcccaaaaaaacaaaaaaaaaaaaaacccccaaaaaaaaaaaccccaaaaccccaaaaacccccccaaaaaacaaaaaaacccccccccccccccaaaiiiqqqtttxxxxxxxyyyyyyvvqqqmmmdddcccc
+SbcccaacccaccccaaacacccaaacccccccccaaaaaaaaacccaccaccccaaaaaaccccccaaccaacccaaaaaccccccccccccccccaaiiiiqqtttxxxxEzzzyyyyvvvqqqmmmddccccc
+abccaaaccccccccaaccccccccccccccccccaaaaaaaaccccccccccccaaaaaaccccccccccccccaaacaaaccaacccccccccccccciiiqqqttttxxxyyyyyvvvvqqqmmmdddccccc
+abccccccccccccccccccccccccccccccccaaaaaaaccccccccccccccaaaaaacccccccccccccccaacccccaaaaaaaccccccccccciiiqqqttttxxyyyyyvvvrrrnnneeecccccc
+abcaaaaccccccccccccccccccccccccccaaaaaaaaccccccccccccccccaacccccccccccccccccccccccccaaaaacccccccccccciiiqqqqttxxyyyyyyyvvrrnnnneeecccccc
+abcaaaaacccccccccccccccccccccccccaaaacaaacccaccaaacccccccccccccccccccccccccaaaccccaaaaaaaccccccccccccciiiqqqttwwyywwyyywwrrnnneeeccccccc
+abaaaaaacccaccaccccccccccccccccccaaaaccaacccaaaaaaccccccccccccccccaaaccccaaaaaacccaaaaaaaacccccccccccciiiqqqtswwwwwwwwwwwrrnnneeeccccccc
+abaaaaaacccaaaaccccccccaaaacccccccaaacccccccaaaaaacccccccccccccccaaaaaaccaaaaaacccaaaaaaaacaaccccccaaciiiqppsswwwwsswwwwwrrrnneeeccccccc
+abcaaaaacccaaaaacccccccaaaacccccccccccccccccaaaaaaaccccccccccccccaaaaaaccaaaaaacccccaaaaaaaaaccccccaaaahhpppssswwsssswwwwrrrnneeeacccccc
+abcaaaccccaaaaaacccccccaaaaccccccccccccccccaaaaaaaaccccccccccccccaaaaacccaaaaaccccccaacaaaaaaaaccaaaaaahhpppsssssssssrrrrrrnnneeeacccccc
+abccccccccaaaaaaccccccccaacccccccccccccccccaaaaaaaaccccaacccccccccaaaaaccaaaaacccccccccaaaaaaaaccaaaaachhpppssssssoosrrrrrrnnneeeaaacccc
+abccccccccccaaccccccccccccccccaaaaaccccccaacccaaacccaaaaacccccccccaacaacccccccccccccccccaaaaaaacccaaaaahhhppppssppooooorroonnffeaaaacccc
+abaaccccccccccccccccccccccccccaaaaaccccccaacccaaaccccaaaaacccccccccccccccccccccccccccaacaaaaacccccaacaahhhppppppppoooooooooonfffaaaacccc
+abaccccccccccccccccccccccccccaaaaaacccaaaaaaaacccccccaaaaaccccccccccccccccccccccccaaaaaaaaaaaccccccccccchhhpppppppgggoooooooffffaacccccc
+abaccccccccccccccccccccccccccaaaaaacccaaaaaaaaccccccaaaaaccccccacccaacccccccccccccaaaaaccccaaccccccccccchhhhhhggggggggfffffffffaaacccccc
+abaacccccccccccccccccccccccccaaaaaacccccaaaacccccccccaaaacccaacaacaaacccccccccccccaaaaaaacccccccccccccccchhhhgggggggggffffffffccaacccccc
+abcccccccaacccccccccccccccccccaaaccccccaaaaaccccccccaaaaccaaaacaaaaacccccccccccccaaaaaaaaccccccccccccccccchhhggggaaaagffffffcccccccccccc
+abcccccccaacccccccccccccaacccccccccccccaaaaaaccaaccccaaaaaaaaacaaaaaacccccccaaaacaaaaaaaacccccccccccaacccccccaaaacaaaacccccccccccccccccc
+abccccaaaaaaaacccccccaacaaaccccccccccccaaccaacaaaacccaaaaaaaacaaaaaaaaccccccaaaaccacaaaccaaaccccaaaaaacccccccaacccaaaacccccccccccccaaaaa
+abccccaaaaaaaacccccccaaaaaccccccccccccccccccccaaaaccccaaaaaaacaaaaaaaaccccccaaaaccccaaaccaaaaaccaaaaaaaacccccccccccaaaccccccccccccccaaaa
+abccccccaaaaccccccccccaaaaaaccccccccccccccccccaaaacccaaaaaaaaaaccaaccccccccccaacccccccccaaaaacccaaaaaaaacccccccccccaaaccccccccccccccaaaa
+abcccccaaaaaacccccccaaaaaaaacccccccccccccccccccccccaaaaaaaaaaaaaaaacccccccccccccccccccccaaaaaacccaaaaaaaccccccccccccccccccccccccccaaaaaa
diff --git a/day12/src/main.rs b/day12/src/main.rs
index e7a11a9..564abc8 100644
--- a/day12/src/main.rs
+++ b/day12/src/main.rs
@@ -1,3 +1,178 @@
-fn main() {
-    println!("Hello, world!");
+use std::{collections::HashSet, fs::read_to_string};
+
+#[derive(Debug, PartialEq, Eq, Clone, Copy)]
+enum Tile {
+    Start,
+    End,
+    Hight(u8),
+}
+
+impl From<char> for Tile {
+    fn from(input: char) -> Self {
+        match input {
+            'S' => Self::Start,
+            'E' => Self::End,
+            h => Self::Hight(('a'..='z').position(|c| c == h).unwrap() as u8),
+        }
+    }
+}
+
+impl Tile {
+    fn can_move_to(self, other: Tile) -> bool {
+        if let Self::Hight(h1) = self {
+            if let Self::Hight(h2) = other {
+                return h1 + 1 >= h2;
+            }
+        }
+        if self == Self::Start {
+            return other == Self::Hight(0) || other == Self::Hight(1);
+        }
+        if other == Self::End {
+            return self == Self::Hight(('a'..='z').position(|c| c == 'z').unwrap() as u8);
+        }
+        false
+    }
+}
+
+#[derive(Debug, PartialEq, Eq, Clone)]
+struct Map<T> {
+    map: Vec<T>,
+    width: usize,
+    height: usize,
+}
+
+impl From<&str> for Map<Tile> {
+    fn from(input: &str) -> Self {
+        let width = input.lines().map(|line| line.len()).next().unwrap();
+        let height = input.lines().count();
+        let map = input
+            .lines()
+            .flat_map(|line| line.chars().map(Tile::from).collect::<Vec<_>>())
+            .collect::<Vec<_>>();
+        Self { map, width, height }
+    }
+}
+
+impl<T> Map<T> {
+    fn at(&self, point: (usize, usize)) -> &T {
+        let (x, y) = point;
+        let index = x + y * self.width;
+        &self.map[index]
+    }
+
+    fn at_mut(&mut self, point: (usize, usize)) -> &mut T {
+        let (x, y) = point;
+        let index = x + y * self.width;
+        &mut self.map[index]
+    }
+}
+
+fn update(
+    from: (usize, usize),
+    to: (usize, usize),
+    path: &mut Map<Option<u32>>,
+    map: &Map<Tile>,
+    changed: &mut bool,
+) {
+    if !map.at(from).can_move_to(*map.at(to)) {
+        return;
+    }
+
+    let Some(c) = path.at(from) else {return};
+    let cost = path.at(to);
+    let cost = cost.unwrap_or(u32::MAX);
+    if cost <= c + 1 {
+        return;
+    }
+
+    *path.at_mut(to) = Some(c + 1);
+    *changed = true;
+}
+
+fn find_shortest_path(map: &Map<Tile>) -> Option<u32> {
+    let mut path = Map {
+        map: vec![None; map.width * map.height],
+        width: map.width,
+        height: map.height,
+    };
+    let mut start = (0, 0);
+    let mut end = (0, 0);
+    for x in 0..map.width {
+        for y in 0..map.height {
+            match map.at((x, y)) {
+                Tile::Start => start = (x, y),
+                Tile::End => end = (x, y),
+                _ => (),
+            }
+        }
+    }
+    *path.at_mut(start) = Some(0);
+
+    let mut changing = true;
+    while changing {
+        changing = false;
+        for x in 0..map.width {
+            for y in 0..map.height {
+                let point = (x, y);
+                if x != 0 {
+                    update((x - 1, y), point, &mut path, map, &mut changing);
+                }
+                if y != 0 {
+                    update((x, y - 1), point, &mut path, map, &mut changing);
+                }
+                if x != map.width - 1 {
+                    update((x + 1, y), point, &mut path, map, &mut changing);
+                }
+                if y != map.height - 1 {
+                    update((x, y + 1), point, &mut path, map, &mut changing);
+                }
+            }
+        }
+    }
+    *path.at(end)
+}
+
+fn find_best_start(map: &Map<Tile>) -> u32 {
+    let mut start = (0, 0);
+    let mut possible_starts = HashSet::new();
+    for x in 0..map.width {
+        for y in 0..map.height {
+            match map.at((x, y)) {
+                Tile::Start => {
+                    possible_starts.insert((x, y));
+                    start = (x, y);
+                }
+                Tile::Hight(0) => {
+                    possible_starts.insert((x, y));
+                }
+                _ => (),
+            }
+        }
+    }
+    let mut map = map.clone();
+    *map.at_mut(start) = Tile::Hight(0);
+
+    possible_starts
+        .iter()
+        .flat_map(|&start| {
+            let mut map = map.clone();
+            *map.at_mut(start) = Tile::Start;
+            find_shortest_path(&map)
+        })
+        .min()
+        .unwrap()
+}
+
+fn main() {
+    let input = "Sabqponm
+abcryxxl
+accszExk
+acctuvwj
+abdefghi";
+    let input = read_to_string("input.txt").unwrap_or_else(|_| input.to_owned());
+    let map: Map<_> = (&*input).into();
+    let cost = find_shortest_path(&map);
+    println!("{cost:?}");
+    let cost = find_best_start(&map);
+    println!("{cost}");
 }