diff --git a/day12/common.rs b/day12/common.rs
new file mode 100644
index 0000000..c6ef906
--- /dev/null
+++ b/day12/common.rs
@@ -0,0 +1,184 @@
+// Copyright 2022 Christian Ulrich
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+use std::collections::HashSet;
+use std::io;
+
+pub struct Map {
+    squares: Vec<Vec<u8>>,
+    start_pos: (usize, usize),
+    end_pos: (usize, usize),
+}
+
+#[derive(Debug, Clone)]
+struct DijkstraInfo {
+    pos: (usize, usize),
+    shortest_distance: usize,
+    previous: Option<(usize, usize)>,
+}
+
+#[derive(Debug)]
+pub struct ShortestPath {
+    dijkstra_table: Vec<DijkstraInfo>,
+    current: (usize, usize),
+    start_pos: (usize, usize),
+}
+
+impl Map {
+    pub fn from_stdin() -> Result<Self, &'static str> {
+        const ERROR: &str = "cannot parse map";
+        let squares: Result<Vec<Vec<u8>>, _> = io::stdin()
+            .lines()
+            .map(|line| Ok(line.map_err(|_| ERROR)?.into_bytes()))
+            .collect();
+        let mut squares = squares?;
+        let mut start = None;
+        let mut end = None;
+        for y in 0..squares.len() {
+            if squares[y].len() != squares[0].len() {
+                return Err(ERROR);
+            }
+            for x in 0..squares[y].len() {
+                match squares[y][x] as char {
+                    'S' if { start.is_none() } => {
+                        start = Some((x, y));
+                        squares[y][x] = 'a' as u8;
+                    }
+                    'S' if { start.is_some() } => return Err(ERROR),
+                    _ => (),
+                }
+                match squares[y][x] as char {
+                    'E' if { end.is_none() } => {
+                        end = Some((x, y));
+                        squares[y][x] = 'z' as u8;
+                    }
+                    'E' if { end.is_some() } => return Err(ERROR),
+                    _ => (),
+                }
+            }
+        }
+        Ok(Self {
+            squares: squares,
+            start_pos: start.ok_or(ERROR)?,
+            end_pos: end.ok_or(ERROR)?,
+        })
+    }
+
+    pub fn square_height(&self, pos: (usize, usize)) -> Option<u8> {
+        let (x, y) = pos;
+        self.squares.get(y)?.get(x).cloned()
+    }
+
+    pub fn start_pos(&self) -> (usize, usize) {
+        self.start_pos
+    }
+
+    pub fn end_pos(&self) -> (usize, usize) {
+        self.end_pos
+    }
+
+    fn neighbors(&self, pos: (usize, usize)) -> Option<Vec<(usize, usize)>> {
+        let mut result = vec![];
+        let height = self.square_height(pos)?;
+        let (x, y) = pos;
+        if x > 0 {
+            result.push((x - 1, y));
+        }
+        if x < self.squares[0].len() - 1 {
+            result.push((x + 1, y));
+        }
+        if y > 0 {
+            result.push((x, y - 1));
+        }
+        if y < self.squares.len() - 1 {
+            result.push((x, y + 1));
+        }
+        let is_accessible = |pos: (usize, usize)| {
+            let neighbor_height = self.square_height(pos).unwrap();
+            u8::abs_diff(neighbor_height, height) <= 1 || neighbor_height > height
+        };
+        Some(
+            result
+                .iter()
+                .filter(|&pos| is_accessible(*pos))
+                .cloned()
+                .collect(),
+        )
+    }
+
+    fn dijkstra_table(&self, start_pos: (usize, usize)) -> Vec<DijkstraInfo> {
+        let mut result = Vec::with_capacity(self.squares.len() * self.squares[0].len());
+        for y in 0..self.squares.len() {
+            for x in 0..self.squares[0].len() {
+                let info = DijkstraInfo {
+                    pos: (x, y),
+                    shortest_distance: if (x, y) == start_pos { 0 } else { usize::MAX },
+                    previous: None,
+                };
+                result.push(info);
+            }
+        }
+        result
+    }
+
+    pub fn shortest_path(&self) -> ShortestPath {
+        // we reverse start_pos and end_pos so the ShortestPath will have the right order
+        let start_pos = self.end_pos;
+        let end_pos = self.start_pos;
+
+        let mut table = self.dijkstra_table(start_pos);
+        let mut unvisited: HashSet<(usize, usize)> = table.iter().map(|i| i.pos).collect();
+        while let Some(info) = table
+            .iter()
+            .filter(|i| i.shortest_distance < usize::MAX && unvisited.contains(&i.pos))
+            .min_by_key(|i| i.shortest_distance)
+            .cloned()
+        {
+            for neighbor_pos in self.neighbors(info.pos).unwrap() {
+                let neighbor_info = table.iter_mut().find(|n| n.pos == neighbor_pos).unwrap();
+                let distance = info.shortest_distance + 1;
+                if distance < neighbor_info.shortest_distance {
+                    neighbor_info.shortest_distance = distance;
+                    neighbor_info.previous = Some(info.pos);
+                }
+            }
+            unvisited.remove(&info.pos);
+        }
+
+        ShortestPath {
+            dijkstra_table: table,
+            current: end_pos,
+            start_pos: start_pos,
+        }
+    }
+}
+
+impl Iterator for ShortestPath {
+    type Item = (usize, usize);
+
+    fn next(&mut self) -> Option<Self::Item> {
+        if self.current == self.start_pos {
+            return None;
+        }
+        let result = self.current;
+        let info = self
+            .dijkstra_table
+            .iter()
+            .find(|i| i.pos == self.current)
+            .unwrap();
+        self.current = info.previous.unwrap();
+        Some(result)
+    }
+}
diff --git a/day12/input b/day12/input
new file mode 100644
index 0000000..3bff85e
--- /dev/null
+++ b/day12/input
@@ -0,0 +1,41 @@
+abaaaaacaaaacccccccccaaaaaaccccccccccccccccccccccccccccccccccaaaaaa
+abaaaaacaaaaccccaaaaaaaaaacccccccccccccccccccccccccccccccccccaaaaaa
+abaaacccaaaaccccaaaaaaaaaaacccaacccccccccccaacccccccccccccccccaaaaa
+abaaaacccaacccccaaaaaaaaaaaaaaaaacccccccccccacccccccccccccccccccaaa
+abacaacccccccccccaaaaaaaaaaaaaaaaccccccccccaacccccccccccccccccccaaa
+abcccacccccccccccaaaaaaaccaaaaaaaccccccccccclllcccccacccccccccccaac
+abccccccccccccccccaaaaaccccccccccccccccccclllllllcccccccccccccccccc
+abaaacccccccccccccaaaaaccccccccccccccccaakklllllllcccccccccaacccccc
+abaaacccccccccccacccaaaccccccccccccccccakkklpppllllccddaaacaacccccc
+abaaacccaaacccccaacaaaccccccccccccccccckkkkpppppllllcddddaaaacccccc
+abaacccaaaacccccaaaaaccccccccccccccccckkkkpppppppllmmddddddaaaacccc
+abaaaccaaaaccccccaaaaaacaaacccccccccckkkkpppuuuppplmmmmdddddaaacccc
+abaaacccaaaccccaaaaaaaacaaaaccccccckkkkkoppuuuuuppqmmmmmmdddddacccc
+abcccccccccccccaaaaaaaacaaaacccccjkkkkkooppuuuuuuqqqmmmmmmmddddcccc
+abccccccccccccccccaaccccaaaccccjjjjkoooooouuuxuuuqqqqqqmmmmmddecccc
+abacaaccccccccccccaacccccccccccjjjjoooooouuuxxxuvvqqqqqqqmmmeeecccc
+abaaaacccccccacccaccccccccccccjjjjoootuuuuuuxxxyvvvvvqqqqmmmeeecccc
+abaaaaacccccaaacaaacccccccccccjjjoooottuuuuuxxyyvvvvvvvqqmnneeecccc
+abaaaaaccaaaaaaaaaaccccccccaccjjjooottttxxxxxxyyyyyyvvvqqnnneeecccc
+abaaaccccaaaaaaaaaacccccccaaccjjjoootttxxxxxxxyyyyyyvvqqqnnneeecccc
+SbcaaccccaaaaaaaaaaccccaaaaacajjjnnntttxxxxEzzzyyyyvvvrrqnnneeccccc
+abcccccccaaaaaaaaaaacccaaaaaaaajjjnnntttxxxxyyyyyvvvvrrrnnneeeccccc
+abcccccccaaaaaaaaaaacccccaaaaccjjjnnnnttttxxyyyyywvvrrrnnneeecccccc
+abcccccccccaaaaaaccaccccaaaaaccciiinnnnttxxyyyyyyywwrrnnnneeecccccc
+abccccccccccccaaacccccccaacaaaccciiinnnttxxyywwyyywwrrnnnffeccccccc
+abccccccccccccaaacccccccaccaaaccciiinnnttwwwwwwwwwwwrrrnnfffccccccc
+abccccccccccccccccccccccccccccccciiinnnttwwwwsswwwwwrrrnnfffccccccc
+abaaaccaaccccccccccccccccccccccccciinnnttswwwssswwwwrrroofffacccccc
+abaaccaaaaaacccccccccccccccccaaacciinnntssssssssssrrrrooofffacccccc
+abaccccaaaaacccccccaaacccccccaaaaciinnnssssssmmssssrrrooofffacccccc
+abaacaaaaaaacccccccaaaaccccccaaaaciiinmmmssmmmmmoosroooooffaaaacccc
+abaaaaaaaaaaaccccccaaaaccccccaaacciiimmmmmmmmmmmoooooooofffaaaacccc
+abcaaaaaaaaaaccccccaaaaccccccccccccihhmmmmmmmhggoooooooffffaaaccccc
+abcccccaaacaccccccccaaccccccccccccchhhhhhhhhhhggggggggggffaaacccccc
+abaccccaacccccccccccaaaccccccccccccchhhhhhhhhhgggggggggggcaaacccccc
+abaaaccccaccccccccccaaaacccaacccccccchhhhhhhaaaaaggggggcccccccccccc
+abaaaccccaaacaaaccccaaaacaaaacccccccccccccccaaaacccccccccccccccaaac
+abaacccccaaaaaaaccccaaaaaaaaacccccccccccccccaaacccccccccccccccccaaa
+abaaaccccaaaaaaccccaaaaaaaaccccccccccccccccccaacccccccccccccccccaaa
+abccccccaaaaaaaaaaaaaaaaaaacccccccccccccccccaaccccccccccccccccaaaaa
+abcccccaaaaaaaaaaaaaaaaaaaaacccccccccccccccccccccccccccccccccaaaaaa
diff --git a/day12/part1.rs b/day12/part1.rs
new file mode 100644
index 0000000..97b979e
--- /dev/null
+++ b/day12/part1.rs
@@ -0,0 +1,26 @@
+// Copyright 2022 Christian Ulrich
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+//
+// usage: ./part1 < input
+
+pub mod common;
+
+use common::Map;
+
+fn main() -> Result<(), &'static str> {
+    let map = Map::from_stdin()?;
+    println!("{:?}", map.shortest_path().count());
+    Ok(())
+}
diff --git a/day12/testinput b/day12/testinput
new file mode 100644
index 0000000..86e9cac
--- /dev/null
+++ b/day12/testinput
@@ -0,0 +1,5 @@
+Sabqponm
+abcryxxl
+accszExk
+acctuvwj
+abdefghi