diff --git a/src/tasks/day18.rs b/src/tasks/day18.rs
index bc36a15..016c0b0 100644
--- a/src/tasks/day18.rs
+++ b/src/tasks/day18.rs
@@ -5,6 +5,7 @@ use std::collections::HashSet;
 use std::collections::VecDeque;
 use std::rc::Rc;
 
+#[allow(dead_code)]
 pub fn run() {
     let input: Map = Map(std::fs::read_to_string("input/day18.txt")
         .unwrap()
@@ -12,10 +13,13 @@ pub fn run() {
         .map(|line| line.chars().collect_vec())
         .collect_vec());
 
-    task1(input.clone());
+    let t1 = task(input.clone());
+    println!("Task 1: best bound to get all keys is {}", t1);
+    let t2 = task(input.clone().split_robot());
+    println!("Task 2: best bound to get all keys is {}", t2);
 }
 
-fn task1(map: Map) {
+fn task(map: Map) -> usize {
     let mut all_keys = map
         .0
         .iter()
@@ -51,20 +55,18 @@ fn task1(map: Map) {
 
         visited.insert(summary);
     }
-    println!(
-        "Task 1: best bound to get all keys is {}",
-        best_found_for_all
-    );
+
+    best_found_for_all
 }
 
 #[derive(Eq, PartialEq, Hash, Debug)]
-struct StateSummary(Pos, String);
+struct StateSummary(Vec<Pos>, String);
 impl StateSummary {
     fn from(state: &State) -> Self {
         let mut s = state.opened.iter().collect_vec();
         s.sort();
         Self(
-            state.current,
+            state.currents.clone(),
             s.into_iter()
                 .map(|c| {
                     let mut x = *c;
@@ -82,52 +84,96 @@ struct StateSummaryDist(Pos, HashSet<char>, usize);
 struct Map(Vec<Vec<char>>);
 
 impl Map {
-    fn coordinate_of(&self, symbol: char) -> Pos {
+    fn coordinate_of(&self, symbol: char) -> Vec<Pos> {
         self.0
             .iter()
             .enumerate()
-            .map(|(y, line)| {
+            .fold(Vec::new(), |vec, (y, line)| {
                 line.iter()
                     .enumerate()
-                    .find(|(_x, c)| **c == symbol)
-                    .map(|(x, _c)| Pos(x, y))
+                    .filter(|(_x, c)| **c == symbol)
+                    .fold(vec, |mut vec, (x, _c)| {
+                        vec.push(Pos(x, y));
+                        vec
+                    })
             })
-            .find(|op| op.is_some())
-            .unwrap()
-            .unwrap()
     }
 
-    fn reachable_keys(&self, start: Pos, open_doors: &HashSet<char>) -> Vec<(char, usize, Pos)> {
+    /**
+     * return: (char: found key, usize1: index of moved robot,
+     * usize2: distance that robot moved, Pos: new position of robot[index]),
+     * usize3: number of empty points on path to last_door_opened
+     */
+    fn reachable_keys(
+        &self,
+        start_points: Vec<Pos>,
+        open_doors: &HashSet<char>,
+        last_door_opened: Option<char>,
+    ) -> Vec<(char, usize, usize, Pos, usize)> {
         let all_keys = 'a'..='z';
-        let mut result = vec![];
 
-        let mut open: VecDeque<(Pos, usize)> = VecDeque::new();
-        open.push_back((start, 0));
-        let mut visited: HashSet<Pos> = HashSet::new();
-        while let Some((current, walked)) = open.pop_front() {
-            if visited.contains(&current) {
-                continue;
-            }
-            let field = self.0[current.1][current.0];
-            let field_is_key = all_keys.contains(&field);
-            // if can move over current type: push neighbors to open
-            if field == '.' || field == '@' || open_doors.contains(&field) || field_is_key {
-                current
-                    .neighbors()
-                    .iter()
-                    .for_each(|n| open.push_back((*n, walked + 1)));
+        let bfs = |start: Pos, open_doors: &HashSet<char>| {
+            // key, distance, new_pos, number of steps of distance until last_open door is met
+            let mut result: Vec<(char, usize, Pos, usize)> = vec![];
+            let mut open: VecDeque<(Pos, usize, usize)> = VecDeque::new(); //position, distance form start, distance until last door opened is met
+            open.push_back((start, 0, 0));
+            let mut visited: HashSet<Pos> = HashSet::new();
+            while let Some((current, walked, ldod)) = open.pop_front() {
+                if visited.contains(&current) {
+                    continue;
+                }
+                let field = self.0[current.1][current.0];
+                let field_is_key = all_keys.contains(&field);
+                // if can move over current type: push neighbors to open
+                if field == '.' || field == '@' || open_doors.contains(&field) || field_is_key {
+                    let mut ldod = 0;
+                    if let Some(ldo) = last_door_opened {
+                        if ldo == field {
+                            ldod = walked;
+                        }
+                    };
+                    current
+                        .neighbors()
+                        .iter()
+                        .for_each(|n| open.push_back((*n, walked + 1, ldod)));
+                }
+
+                // if it is a key: push it to result
+                if field_is_key {
+                    result.push((field, walked, current, ldod));
+                }
+
+                // anyways: push to visited
+                visited.insert(current);
             }
 
-            // if it is a key: push it to result
-            if field_is_key {
-                result.push((field, walked, current));
-            }
+            result
+        };
 
-            // anyways: push to visited
-            visited.insert(current);
-        }
+        start_points
+            .iter()
+            .enumerate()
+            .flat_map(|(robot_i, robot_pos)| {
+                bfs(*robot_pos, open_doors)
+                    .into_iter()
+                    .map(|(key, dist, final_pos, ldod)| (key, robot_i, dist, final_pos, ldod))
+                    .collect_vec()
+            })
+            .collect_vec()
+    }
 
-        result
+    fn split_robot(mut self) -> Self {
+        let Pos(x, y) = self.coordinate_of('@')[0];
+        self.0[x][y] = '#';
+        self.0[x - 1][y - 1] = '@';
+        self.0[x - 1][y] = '#';
+        self.0[x - 1][y + 1] = '@';
+        self.0[x + 1][y] = '#';
+        self.0[x + 1][y + 1] = '@';
+        self.0[x][y - 1] = '#';
+        self.0[x + 1][y - 1] = '@';
+        self.0[x][y + 1] = '#';
+        self
     }
 }
 
@@ -147,19 +193,25 @@ impl Pos {
 
 #[derive(Eq, PartialEq)]
 struct State {
-    current: Pos,
+    currents: Vec<Pos>,
+    underrun: Vec<usize>, // the number of steps a robot is behind the leading robots steps
     opened: HashSet<char>, // capital letter
     map: Rc<Map>,
     steps_taken: usize,
+    last_door_opened: Option<char>,
 }
 
 impl State {
     fn new(map: Rc<Map>) -> Self {
+        let currents = map.coordinate_of('@');
+        let no_robots = currents.len();
         Self {
-            current: map.coordinate_of('@'),
+            currents: currents,
+            underrun: std::iter::repeat(0).take(no_robots).collect_vec(),
             opened: HashSet::new(),
             map: map,
             steps_taken: 0,
+            last_door_opened: None,
         }
     }
 
@@ -167,9 +219,9 @@ impl State {
         // find all keys that are not yet collected + their distance + position
         let next_keys = self
             .map
-            .reachable_keys(self.current, &self.opened)
+            .reachable_keys(self.currents.clone(), &self.opened, self.last_door_opened)
             .into_iter()
-            .filter(|(key, _, _)| {
+            .filter(|(key, _, _, _, _)| {
                 let mut c = *key;
                 c.make_ascii_uppercase();
                 !self.opened.contains(&c)
@@ -179,20 +231,52 @@ impl State {
         // create new state with one open door added + steps increased + current position updated
         next_keys
             .into_iter()
-            .map(|(key, distance, current)| self.advance(key, distance, current))
+            .map(|(key, robot_i, distance, current, ldod)| {
+                self.advance(key, robot_i, distance, current, ldod)
+            })
             .collect_vec()
     }
 
-    fn advance(&self, key_added: char, additional_steps: usize, new_pos: Pos) -> Self {
+    fn advance(
+        &self,
+        key_added: char,
+        robot_index: usize,
+        additional_steps: usize,
+        new_pos: Pos,
+        ldod: usize,
+    ) -> Self {
         let mut open_doors = self.opened.clone();
         let mut door = key_added;
         door.make_ascii_uppercase();
         open_doors.insert(door);
+        let mut positions = self.currents.clone();
+        positions[robot_index] = new_pos;
+        let underrun = self
+            .underrun
+            .iter()
+            .enumerate()
+            .map(|(i, u)| {
+                if i != robot_index {
+                    *u + additional_steps
+                } else {
+                    0
+                }
+            })
+            .collect();
+
+        let usable_underrun = if self.underrun[robot_index] >= ldod {
+            ldod
+        } else {
+            self.underrun[robot_index]
+        };
+        let steps_diff = additional_steps - usable_underrun;
         Self {
-            current: new_pos,
+            currents: positions,
+            underrun: underrun,
             opened: open_doors,
             map: self.map.clone(),
-            steps_taken: self.steps_taken + additional_steps,
+            steps_taken: self.steps_taken + steps_diff as usize,
+            last_door_opened: Some(key_added),
         }
     }
 }