diff --git a/10/src/main.rs b/10/src/main.rs
index 80c4c6b..5484140 100644
--- a/10/src/main.rs
+++ b/10/src/main.rs
@@ -18,20 +18,25 @@ fn main() {
 // PARSE
 
 #[derive(Debug)]
-struct PipeSection {
+struct MapCell {
     dist: u64,
     kind: char,
+    inside: bool,
 }
 
-impl From<char> for PipeSection {
+impl From<char> for MapCell {
     fn from(c: char) -> Self {
-        PipeSection { dist: 0, kind: c }
+        MapCell {
+            dist: 0,
+            kind: c,
+            inside: false,
+        }
     }
 }
 
 #[derive(Debug)]
 struct PipeMap {
-    map: Vec<Vec<PipeSection>>,
+    map: Vec<Vec<MapCell>>,
     start: (usize, usize),
 }
 
@@ -100,15 +105,87 @@ impl PipeMap {
                 }
             }
         }
+
         [adj_positions[0], adj_positions[1]]
     }
+
+    fn mark_inside(&mut self) {
+        let start_adj = self.start_adjacencies();
+
+        let start_kind = if start_adj.contains(
+            &self
+                .apply_adj(self.start, (0, -1))
+                .unwrap_or((99999, 99999)),
+        ) && start_adj
+            .contains(&self.apply_adj(self.start, (0, 1)).unwrap_or((99999, 99999)))
+        {
+            '|'
+        } else if start_adj.contains(
+            &self
+                .apply_adj(self.start, (-1, 0))
+                .unwrap_or((99999, 99999)),
+        ) && start_adj
+            .contains(&self.apply_adj(self.start, (1, 0)).unwrap_or((99999, 99999)))
+        {
+            '-'
+        } else if start_adj.contains(
+            &self
+                .apply_adj(self.start, (0, -1))
+                .unwrap_or((99999, 99999)),
+        ) && start_adj
+            .contains(&self.apply_adj(self.start, (1, 0)).unwrap_or((99999, 99999)))
+        {
+            'L'
+        } else if start_adj.contains(
+            &self
+                .apply_adj(self.start, (0, -1))
+                .unwrap_or((99999, 99999)),
+        ) && start_adj.contains(
+            &self
+                .apply_adj(self.start, (-1, 0))
+                .unwrap_or((99999, 99999)),
+        ) {
+            'J'
+        } else if start_adj.contains(&self.apply_adj(self.start, (0, 1)).unwrap_or((99999, 99999)))
+            && start_adj.contains(
+                &self
+                    .apply_adj(self.start, (-1, 0))
+                    .unwrap_or((99999, 99999)),
+            )
+        {
+            '7'
+        } else if start_adj.contains(&self.apply_adj(self.start, (0, 1)).unwrap_or((99999, 99999)))
+            && start_adj.contains(&self.apply_adj(self.start, (1, 0)).unwrap_or((99999, 99999)))
+        {
+            'F'
+        } else {
+            panic!("invalid start");
+        };
+
+        for row in &mut self.map {
+            let mut inside = false;
+            for cell in row {
+                let mut kind = cell.kind;
+                if cell.dist == 0 && kind != 'S' {
+                    cell.inside = inside;
+                } else {
+                    if kind == 'S' {
+                        kind = start_kind;
+                    }
+                    if kind == '|' || kind == 'L' || kind == 'J' {
+                        inside = !inside;
+                    }
+                }
+            }
+        }
+    }
 }
 
 impl<T: BufRead> From<Lines<T>> for PipeMap {
     fn from(lines: Lines<T>) -> Self {
-        let mut map: Vec<Vec<PipeSection>> = Vec::new();
+        let mut map: Vec<Vec<MapCell>> = Vec::new();
         for line in lines {
-            map.push(line.unwrap().chars().map(PipeSection::from).collect());
+            map.push(line.unwrap().chars().map(MapCell::from).collect());
         }
 
         let start = map
@@ -123,7 +200,7 @@ impl<T: BufRead> From<Lines<T>> for PipeMap {
 
         let mut cur_positions = pipemap.start_adjacencies();
         let mut cur_distance = 1;
-        loop {  
+        loop {
             for pos in cur_positions {
                 pipemap.map[pos.1][pos.0].dist = cur_distance;
             }
@@ -163,12 +240,39 @@ impl<T: BufRead> From<Lines<T>> for PipeMap {
 fn problem1<T: BufRead>(input: Lines<T>) -> u64 {
     let map = PipeMap::from(input);
 
-    map.map.iter().map(|row| row.iter().map(|cell| cell.dist).max().unwrap()).max().unwrap()
+    map.map
+        .iter()
+        .map(|row| row.iter().map(|cell| cell.dist).max().unwrap())
+        .max()
+        .unwrap()
 }
 
 // PROBLEM 2 solution
 fn problem2<T: BufRead>(input: Lines<T>) -> u64 {
-    0
+    let mut map = PipeMap::from(input);
+    map.mark_inside();
+
+    for row in &map.map {
+        for cell in row {
+            print!("{}", cell.kind);
+        }
+        print!(" ");
+        for cell in row {
+            print!(
+                "{}",
+                match cell.inside {
+                    true => 'I',
+                    false => 'O',
+                }
+            );
+        }
+        println!();
+    }
+
+    map.map
+        .iter()
+        .map(|row| row.iter().filter(|cell| cell.inside).count())
+        .sum::<usize>() as u64
 }
 
 #[cfg(test)]
@@ -182,6 +286,17 @@ SJ.L7
 |F--J
 LJ...";
 
+    const EXAMPLE2: &str = &"FF7FSF7F7F7F7F7F---7
+L|LJ||||||||||||F--J
+FL-7LJLJ||||||LJL-77
+F--JF--7||LJLJ7F7FJ-
+L---JF-JLJ.||-FJLJJ7
+|F|F-JF---7F7-L7L|7|
+|FFJF7L7F-JF7|JL---7
+7-L-JL7||F7|L7F-7F7|
+L.L7LFJ|||||FJL7||LJ
+L7JLJL-JLJLJL--JLJ.L";
+
     #[test]
     fn problem1_example() {
         let c = Cursor::new(EXAMPLE);
@@ -190,7 +305,7 @@ LJ...";
 
     #[test]
     fn problem2_example() {
-        let c = Cursor::new(EXAMPLE);
-        assert_eq!(problem2(c.lines()), 0);
+        let c = Cursor::new(EXAMPLE2);
+        assert_eq!(problem2(c.lines()), 10);
     }
 }