diff --git a/2023/src/day04.rs b/2023/src/day04.rs
new file mode 100644
index 0000000..d274580
--- /dev/null
+++ b/2023/src/day04.rs
@@ -0,0 +1,113 @@
+use aoc_runner_derive::{aoc, aoc_generator};
+use std::collections::HashSet;
+
+#[derive(Debug)]
+struct Card {
+    id: usize,
+    winning: HashSet<u32>,
+    present: HashSet<u32>,
+}
+
+impl Card {
+    fn matching_numbers(&self) -> Vec<&u32> {
+        self.winning
+            .intersection(&self.present)
+            .collect::<Vec<&u32>>()
+    }
+}
+
+#[aoc_generator(day4)]
+fn parse(input: &str) -> Vec<Card> {
+    input
+        .lines()
+        .filter_map(|line| {
+            if !line.is_empty() {
+                let cparts: Vec<&str> = line.split(": ").collect();
+                let id = cparts[0]
+                    .split(" ")
+                    .collect::<Vec<&str>>()
+                    .last()?
+                    .trim_start()
+                    .parse::<usize>()
+                    .unwrap();
+                let cnums: Vec<&str> = cparts[1].split(" | ").collect();
+                let winning: HashSet<u32> = cnums[0]
+                    .replace("  ", " ")
+                    .trim_start()
+                    .split(" ")
+                    .map(|n| n.parse::<u32>().unwrap())
+                    .collect();
+                let present: HashSet<u32> = cnums[1]
+                    .replace("  ", " ")
+                    .trim_start()
+                    .split(" ")
+                    .map(|n| n.parse::<u32>().unwrap())
+                    .collect();
+                Some(Card {
+                    id,
+                    winning,
+                    present,
+                })
+            } else {
+                None
+            }
+        })
+        .collect()
+}
+
+#[aoc(day4, part1)]
+fn part1(input: &[Card]) -> i32 {
+    let mut sum = 0;
+    let base: i32 = 2;
+    for c in input.iter() {
+        let m = c.matching_numbers();
+        if m.is_empty() {
+            continue;
+        }
+        let p = base.pow(m.len() as u32 - 1);
+        if m.len() > 0 {
+            sum += p;
+        }
+    }
+    sum
+}
+
+#[aoc(day4, part2)]
+fn part2(input: &[Card]) -> u32 {
+    let mut cards: [u32; 202] = [1; 202];
+    for i in input.len()..cards.len() {
+        cards[i] = 0;
+    }
+    for c in input.iter() {
+        let m = c.matching_numbers();
+        let cur = c.id - 1;
+        for i in 1..=m.len() {
+            let dest = cur + i;
+            if dest >= input.len() {
+                continue;
+            }
+            cards[dest] += cards[cur];
+        }
+    }
+    cards.iter().sum()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const SAMPLE_DATA: &'static str = r#"Card 1: 41 48 83 86 17 | 83 86  6 31 17  9 48 53
+Card 2: 13 32 20 16 61 | 61 30 68 82 17 32 24 19
+Card 3:  1 21 53 59 44 | 69 82 63 72 16 21 14  1
+Card 4: 41 92 73 84 69 | 59 84 76 51 58  5 54 83
+Card 5: 87 83 26 28 32 | 88 30 70 12 93 22 82 36
+Card 6: 31 18 13 56 72 | 74 77 10 23 35 67 36 11
+"#;
+
+    #[test]
+    fn sample_data() {
+        let cards = parse(&SAMPLE_DATA);
+        assert_eq!(part1(&cards), 13);
+        assert_eq!(part2(&cards), 30);
+    }
+}
diff --git a/2023/src/lib.rs b/2023/src/lib.rs
index 8f30b5d..c0e7712 100644
--- a/2023/src/lib.rs
+++ b/2023/src/lib.rs
@@ -3,5 +3,6 @@ use aoc_runner_derive::aoc_lib;
 mod day01;
 mod day02;
 mod day03;
+mod day04;
 
 aoc_lib! { year = 2023 }