diff --git a/d04/Cargo.lock b/d04/Cargo.lock
new file mode 100644
index 0000000..58fc4f8
--- /dev/null
+++ b/d04/Cargo.lock
@@ -0,0 +1,7 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "d04"
+version = "0.1.0"
diff --git a/d04/Cargo.toml b/d04/Cargo.toml
new file mode 100644
index 0000000..314f0c1
--- /dev/null
+++ b/d04/Cargo.toml
@@ -0,0 +1,8 @@
+[package]
+name = "d04"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
diff --git a/d04/input.txt b/d04/input.txt
new file mode 100644
index 0000000..ced5698
--- /dev/null
+++ b/d04/input.txt
@@ -0,0 +1,601 @@
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diff --git a/d04/input_sample.txt b/d04/input_sample.txt
new file mode 100644
index 0000000..669a51d
--- /dev/null
+++ b/d04/input_sample.txt
@@ -0,0 +1,19 @@
+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
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+
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+
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+22 11 13  6  5
+ 2  0 12  3  7
diff --git a/d04/src/main.rs b/d04/src/main.rs
new file mode 100644
index 0000000..509a4eb
--- /dev/null
+++ b/d04/src/main.rs
@@ -0,0 +1,199 @@
+use std::collections::HashSet;
+use std::fmt;
+use std::fs;
+
+#[derive(Debug, Default, Clone, Copy)]
+struct BingoBoard {
+    values: [[usize; 5]; 5],
+    called: [[bool; 5]; 5],
+}
+
+impl BingoBoard {
+    fn build_board(input: &[&str]) -> Self {
+        let mut values = [[0; 5]; 5];
+        for (i, l) in input.iter().enumerate() {
+            for (j, v) in l
+                .split_whitespace()
+                .map(|n| {
+                    n.parse::<usize>()
+                        .expect(format!("Could not parse {}", n).as_str())
+                })
+                .enumerate()
+            {
+                values[i][j] = v;
+            }
+        }
+
+        BingoBoard {
+            values: values,
+            called: [[false; 5]; 5],
+        }
+    }
+
+    fn mark_board(&mut self, number: usize) {
+        for (r, row) in self.values.iter().enumerate() {
+            for (c, value) in row.iter().enumerate() {
+                if *value == number {
+                    self.called[r][c] = true
+                }
+            }
+        }
+    }
+
+    // does winning things
+    fn is_winner(&self) -> bool {
+        // Check rows
+        if self.called.iter().any(|row| row.iter().all(|sq| *sq)) {
+            return true;
+        }
+
+        let board_size = self.called.len();
+        for col in 0..board_size {
+            if self.called.iter().all(|row| row[col]) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
+    fn sum_unmarked(self) -> usize {
+        self.values
+            .iter()
+            .flatten()
+            .zip(self.called.iter().flatten())
+            .map(|pair| {
+                let (val, called) = pair;
+                if *called {
+                    0
+                } else {
+                    *val
+                }
+            })
+            .reduce(|acc, v| acc + v)
+            .unwrap()
+    }
+}
+
+impl fmt::Display for BingoBoard {
+    // This trait requires `fmt` with this exact signature.
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        // Write strictly the first element into the supplied output
+        // stream: `f`. Returns `fmt::Result` which indicates whether the
+        // operation succeeded or failed. Note that `write!` uses syntax which
+        // is very similar to `println!`.
+
+        let message = self
+            .values
+            .iter()
+            .zip(self.called.iter())
+            .map(|x| {
+                let (val_row, called_row) = x;
+                val_row
+                    .iter()
+                    .zip(called_row.iter())
+                    .map(|v| {
+                        let (val, called) = v;
+                        let result: String;
+                        if *called {
+                            result = format!("[{}]", val);
+                        } else {
+                            result = format!("{}", val);
+                        }
+
+                        format!("{: >5}", result)
+                    })
+                    .collect::<Vec<String>>()
+                    .join("")
+            })
+            .collect::<Vec<String>>()
+            .join("\n");
+        write!(f, "{}", message)
+    }
+}
+
+fn part1() {
+    let file_contents = fs::read_to_string("input.txt").expect("No input found");
+    let mut lines = file_contents.lines();
+
+    let numbers: Vec<usize> = lines
+        .next()
+        .expect("No line found in input")
+        .split(",")
+        .map(|n| n.parse().expect(format!("Unknown number: {}", n).as_str()))
+        .collect();
+
+    let board_input: Vec<&str> = lines.filter(|l| l != &"").collect();
+
+    let mut boards: Vec<BingoBoard> = board_input
+        .chunks(5)
+        .map(|c| BingoBoard::build_board(c))
+        .collect();
+
+    let mut score = 0;
+    for (turn, num) in numbers.iter().enumerate() {
+        println!("Turn {}: Called {}", turn, num);
+        for (board_num, board) in boards.iter_mut().enumerate() {
+            board.mark_board(*num);
+            println!("Board {}\n{}\n", board_num, board);
+            if board.is_winner() {
+                println!("Winner!");
+                score = board.sum_unmarked() * num;
+                break;
+            }
+        }
+        if score != 0 {
+            println!("Final score is {}", score);
+            break;
+        }
+    }
+}
+
+fn part2() {
+    let file_contents = fs::read_to_string("input.txt").expect("No input found");
+    let mut lines = file_contents.lines();
+
+    let numbers: Vec<usize> = lines
+        .next()
+        .expect("No line found in input")
+        .split(",")
+        .map(|n| n.parse().expect(format!("Unknown number: {}", n).as_str()))
+        .collect();
+
+    let board_input: Vec<&str> = lines.filter(|l| l != &"").collect();
+
+    let mut boards: Vec<BingoBoard> = board_input
+        .chunks(5)
+        .map(|c| BingoBoard::build_board(c))
+        .collect();
+
+    let mut score = 0;
+    let mut winners = HashSet::new();
+    for (turn, num) in numbers.iter().enumerate() {
+        println!("Turn {}: Called {}", turn, num);
+        for (board_num, board) in boards.iter_mut().enumerate() {
+            // Skip existing winners
+            if winners.contains(&board_num) {
+                continue;
+            }
+            board.mark_board(*num);
+            println!("Board {}\n{}\n", board_num, board);
+            if board.is_winner() {
+                score = board.sum_unmarked() * num;
+                println!("Winner! Score {}", score);
+                winners.insert(board_num);
+            }
+        }
+        if winners.len() == boards.len() {
+            break;
+        }
+    }
+    if score != 0 {
+        println!("Final score is {}", score);
+    }
+}
+
+fn main() {
+    part1();
+    part2();
+}