diff --git a/aoc_2025/src/day3.rs b/aoc_2025/src/day3.rs
new file mode 100644
index 0000000..653199a
--- /dev/null
+++ b/aoc_2025/src/day3.rs
@@ -0,0 +1,100 @@
+use std::iter::Sum;
+
+use crate::{AoC, Day, SimpleDay, WinnowDay};
+use winnow::{
+    Parser, Result,
+    ascii::newline,
+    combinator::{repeat, terminated},
+    error::ContextError,
+    token::one_of,
+};
+
+fn day() -> impl WinnowDay {
+    AoC::new(parse as _, part1 as _, part2 as _)
+}
+
+fn parse<'a, 'b>(input: &'a mut &'b str) -> Result<Vec<Vec<usize>>> {
+    repeat(1.., parse_line).parse_next(input)
+}
+
+fn parse_line(input: &mut &str) -> Result<Vec<usize>, ContextError> {
+    terminated(
+        repeat(
+            1..,
+            one_of(('0'..='9',)).map(|c: char| c.to_string().parse::<usize>().unwrap()),
+        ),
+        newline,
+    )
+    .parse_next(input)
+}
+
+fn part1(input: Vec<Vec<usize>>) -> usize {
+    input.iter().map(joltage(2)).sum()
+}
+
+fn part2(input: Vec<Vec<usize>>) -> usize {
+    input.iter().map(joltage(12)).sum()
+}
+
+fn joltage<
+    'a,
+    B: IntoIterator<IntoIter = I> + Copy,
+    I: ExactSizeIterator<Item = &'a N>,
+    N: Sum<&'a N> + Into<usize> + From<usize> + Copy + Default + 'a,
+>(
+    size: usize,
+) -> impl Fn(B) -> N {
+    move |line| {
+        (line.into_iter().len() - size..line.into_iter().len())
+            .fold((0, 0), |(start, val), end| {
+                line.into_iter()
+                    .enumerate()
+                    .skip(start)
+                    .take(end - start + 1)
+                    .map(|(i, v)| (i + 1, (*v).into() + val * 10))
+                    .reduce(|a, b| if a.1 >= b.1 { a } else { b })
+                    .unwrap()
+            })
+            .1
+            .into()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn part1_test() {
+        day().assert1(
+            "987654321111111
+811111111111119
+234234234234278
+818181911112111
+",
+            "357",
+        );
+    }
+
+    #[test]
+    fn part1_solve() {
+        day().assert1(include_str!("../input/day3.txt"), "17343");
+    }
+
+    #[test]
+    fn part2_test() {
+        day().assert2(
+            "987654321111111
+811111111111119
+234234234234278
+818181911112111
+",
+            "3121910778619",
+        );
+    }
+
+    #[test]
+    fn part2_solve() {
+        day().assert2(include_str!("../input/day3.txt"), "172664333119298");
+    }
+}
diff --git a/aoc_2025/src/lib.rs b/aoc_2025/src/lib.rs
index 3e99aa9..435b796 100644
--- a/aoc_2025/src/lib.rs
+++ b/aoc_2025/src/lib.rs
@@ -7,6 +7,7 @@ use winnow::Parser;
 
 mod day1;
 mod day2;
+mod day3;
 
 trait Day {
     fn assert1(&self, input: &str, output: &str);