diff --git a/input/day04 b/input/day04
new file mode 100644
index 0000000..2354ec0
--- /dev/null
+++ b/input/day04
@@ -0,0 +1,601 @@
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
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+
+ 2 16 13 57 32
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+94 43 51 20 60
\ No newline at end of file
diff --git a/src/day04.rs b/src/day04.rs
new file mode 100644
index 0000000..8c54df9
--- /dev/null
+++ b/src/day04.rs
@@ -0,0 +1,227 @@
+use crate::Day;
+
+#[derive(Clone)]
+pub struct Day04 {
+    numbers: Vec<u32>,
+    boards: Vec<Board>,
+}
+
+#[derive(Clone, Eq, PartialEq, Debug)]
+struct Board(Vec<Vec<Option<u32>>>);
+
+impl Day for Day04 {
+    fn init(content: String) -> Self where Self: Sized {
+        let mut l = content.lines().collect::<Vec<&str>>();
+        let first = l[0];
+        let a = l.drain(0..2);
+        drop(a);
+        let nums = first.split(',').map(|x| x.parse::<u32>().expect("wat?")).collect();
+
+        let split = l.split(|x| x.is_empty());
+        let mut boards = vec![];
+        for vecs in split {
+            let mut rows = vec![];
+            for vec in vecs {
+                let v = vec.split_ascii_whitespace().map(|x| x.parse::<u32>().expect("foo")).map(Option::Some).collect();
+                rows.push(v);
+            }
+            boards.push(Board(rows));
+        }
+
+
+        Day04 {
+            numbers: nums,
+            boards,
+        }
+    }
+
+    fn part1(&self) -> String {
+        let z = self.clone();
+        let mut boards = z.boards;
+        for number in z.numbers {
+            for board in &mut boards {
+                let res = board.mark(number);
+                if res {
+                    let s = board.unmarked_sum();
+                    return format!("{}", s * number);
+                }
+            }
+        }
+
+        panic!("no board can win?")
+    }
+
+    fn part2(&self) -> String {
+        let z = self.clone();
+        let mut boards = z.boards.iter().cloned().map(Option::Some).collect::<Vec<Option<Board>>>();
+        for number in z.numbers {
+            let some_count = boards.iter().map(|x| if x.is_some() { 1 } else { 0 }).sum::<u32>();
+            #[allow(clippy::manual_flatten)]
+            for boardd in &mut boards {
+                if let Some(board) = boardd {
+                    let res = board.mark(number);
+                    if res {
+                        if some_count == 1 {
+                            let s = board.unmarked_sum();
+                            return format!("{}", s * number);
+                        }
+                        *boardd = None;
+                    }
+                }
+            }
+        }
+
+        panic!("no board can win?")
+    }
+}
+
+impl Board {
+    fn mark(&mut self, num: u32) -> bool {
+        #[allow(clippy::manual_flatten)]
+        for columns in &mut self.0 {
+            for row in columns.iter_mut() {
+                if let Some(v) = row {
+                    if *v == num {
+                        *row = None;
+                    }
+                }
+            }
+        }
+        self.check_rows() || self.check_columns()
+    }
+
+    fn check_rows(&self) -> bool {
+        for columns in &self.0 {
+            if columns.iter().all(Option::is_none) {
+                return true;
+            }
+        }
+        false
+    }
+    fn check_columns(&self) -> bool {
+        let t = Board::transpose(&self.0);
+        for rows in t {
+            if rows.iter().all(Option::is_none) {
+                return true;
+            }
+        }
+        false
+    }
+
+    fn transpose<T: Clone>(v: &[Vec<T>]) -> Vec<Vec<T>> {
+        assert!(!v.is_empty());
+        let len = v[0].len();
+        let mut iters: Vec<_> = v.iter().map(|n| n.iter()).collect();
+        (0..len)
+            .map(|_| {
+                iters
+                    .iter_mut()
+                    .map(|n| n.next().unwrap())
+                    .cloned()
+                    .collect::<Vec<T>>()
+            })
+            .collect()
+    }
+
+    fn unmarked_sum(&self) -> u32 {
+        self.0.iter().map(|x| x.iter().flatten().sum::<u32>()).sum()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::fs::read_to_string;
+    use crate::Day04;
+    use crate::day04::Board;
+    use crate::day::Day;
+
+
+    const INPUT: &str = r"7,4,9,5,11,17,23,2,0,14,21,24,10,16,13,6,15,25,12,22,18,20,8,19,3,26,1
+
+22 13 17 11  0
+ 8  2 23  4 24
+21  9 14 16  7
+ 6 10  3 18  5
+ 1 12 20 15 19
+
+ 3 15  0  2 22
+ 9 18 13 17  5
+19  8  7 25 23
+20 11 10 24  4
+14 21 16 12  6
+
+14 21 17 24  4
+10 16 15  9 19
+18  8 23 26 20
+22 11 13  6  5
+ 2  0 12  3  7";
+
+    #[test]
+    fn board_mark_test() {
+        let mut b = Board(vec![vec![Some(10)]]);
+        let res = b.mark(10);
+        assert_eq!(b.0[0][0], None);
+        assert!(res)
+    }
+
+    #[test]
+    fn board_rows_are_marked() {
+        let b = Board(vec![vec![None, None, None, None], vec![Some(10), Some(10), Some(10), Some(10)]]);
+        assert!(b.check_rows())
+    }
+
+    #[test]
+    fn board_rows_are_not_marked() {
+        let b = Board(vec![vec![None, None, Some(10), None]]);
+        assert!(!b.check_rows())
+    }
+
+    #[test]
+    fn board_cols_are_marked() {
+        let b = Board(vec![vec![None], vec![None], vec![None], vec![None]]);
+        assert!(b.check_columns())
+    }
+
+    #[test]
+    fn board_cols_are_not_marked() {
+        let b = Board(vec![vec![None], vec![None], vec![Some(10)], vec![None]]);
+        assert!(!b.check_columns())
+    }
+
+    #[test]
+    fn board_cols_are_not_rows() {
+        let b = Board(vec![vec![None, Some(10)], vec![None, Some(10)], vec![None, Some(10)], vec![None, Some(10)]]);
+        assert!(!b.check_rows())
+    }
+
+    #[test]
+    fn part1_test() {
+        let t = Day04::init(INPUT.to_string());
+        let p1 = t.part1();
+        assert_eq!("4512", p1)
+    }
+
+    #[test]
+    fn part2_test() {
+        let t = Day04::init(INPUT.to_string());
+        let p2 = t.part2();
+        assert_eq!("1924", p2)
+    }
+
+
+    #[test]
+    fn part1_real() {
+        let f = read_to_string("./input/day04").expect("Could not load input");
+        let t = Day04::init(f);
+        let p1 = t.part1();
+        assert_eq!("8136", p1)
+    }
+
+    #[test]
+    fn part2_real() {
+        let f = read_to_string("./input/day04").expect("Could not load input");
+        let t = Day04::init(f);
+        let p2 = t.part2();
+        assert_eq!("12738", p2)
+    }
+}
\ No newline at end of file
diff --git a/src/main.rs b/src/main.rs
index 9d1dfda..58a20c0 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -4,12 +4,14 @@ use clap::{App, Arg};
 use crate::day01::Day01;
 use crate::day02::Day02;
 use crate::day03::Day03;
+use crate::day04::Day04;
 use crate::day::Day;
 
 mod day;
 mod day01;
 mod day02;
 mod day03;
+mod day04;
 
 fn load_input(day: &str) -> String {
     read_to_string(format!("./input/day{}", day)).expect("Could not load input")
@@ -45,7 +47,8 @@ fn main() {
         .get_matches();
 
     let days: Vec<Box<dyn Day>> = vec![Box::new(Day01::init(load_input("01"))), Box::new(Day02::init(load_input("02"))),
-                                       Box::new(Day03::init(load_input("03")))];
+                                       Box::new(Day03::init(load_input("03"))),
+                                       Box::new(Day04::init(load_input("04")))];
 
     let _verbosity = matches.occurrences_of("v");
     if matches.is_present("all") {