diff --git a/src/days.rs b/src/days.rs
index 0958165..21b6c99 100644
--- a/src/days.rs
+++ b/src/days.rs
@@ -1,7 +1,7 @@
 pub mod d1;
 pub mod d2;
 pub mod d3;
-// pub mod d4;
+pub mod d4;
 // pub mod d5;
 // pub mod d6;
 // pub mod d7;
diff --git a/src/days/d4.rs b/src/days/d4.rs
new file mode 100644
index 0000000..70817d8
--- /dev/null
+++ b/src/days/d4.rs
@@ -0,0 +1,118 @@
+#![allow(non_upper_case_globals)]
+use crate::prelude::*;
+
+pub type I = Vec<Vec<char>>;
+pub type O = usize;
+
+fn _parse (data: &str) -> I {
+    data.lines().map(|line| line.chars().collect()).collect()
+}
+
+fn _raycast ((y, x): (usize, usize), rows: usize, cols: usize) -> Vec<Vec<(usize, usize)>> {
+    const r: [[(isize, isize); 3]; 8] = [
+        [(-1, -1), (-2, -2), (-3, -3)], // UL
+        [(-1, 0), (-2, 0), (-3, 0)], // U
+        [(-1, 1), (-2, 2), (-3, 3)], // UR
+
+        [(0, -1), (0, -2), (0, -3)], // L
+        [(0, 1), (0, 2), (0, 3)], // R
+
+
+        [(1, -1), (2, -2), (3, -3)], // DL
+        [(1, 0), (2, 0), (3, 0)], // D
+        [(1, 1), (2, 2), (3, 3)], // DR
+    ];
+
+
+    r.into_iter().filter_map(|e| {
+        let new = e.into_iter().filter_map(|(dy, dx)| {
+            let ny = y.checked_add_signed(dy)?;
+            let nx = x.checked_add_signed(dx)?;
+            if ny >= rows || nx >= cols { return None; }
+            Some((ny, nx))
+        }).collect_vec();
+        if new.len() != 3 { return None }
+        Some(new)
+    }).collect()
+}
+
+fn _raycast_2 ((y, x): (usize, usize), rows: usize, cols: usize) -> Vec<(usize, usize)> {
+    const r: [(isize, isize); 4] = [
+        (-1, -1), // UL
+        (-1, 1), // UR
+        (1, -1), // DL
+        (1, 1), // DR
+    ];
+
+    let v: Vec<(usize, usize)> = r.into_iter().filter_map(|(dy, dx)| {
+        let ny = y.checked_add_signed(dy)?;
+        let nx = x.checked_add_signed(dx)?;
+        if ny >= rows || nx >= cols { return None; }
+        Some((ny, nx))
+    }).collect();
+
+
+    if v.len() != r.len() { vec![] } else { v }
+}
+
+fn _silver (data: I) -> O {
+    let rows = data.len();
+    let mut count = 0;
+    for (y, row) in data.iter().enumerate() {
+        let cols = row.len();
+        for (x, &cell) in row.iter().enumerate() {
+            if cell == 'X' {
+                count += _raycast((y, x), rows, cols).into_iter().map(|e| format!("X{}", e.iter().map(|&(y, x)| data[y][x]).collect::<String>())).filter(|s| s == "XMAS").count();
+            }
+        }
+    }
+
+    count
+}
+
+fn _gold (data: I) -> O {
+    let rows = data.len();
+    let mut count = 0;
+    for (y, row) in data.iter().enumerate() {
+        let cols = row.len();
+        for (x, &cell) in row.iter().enumerate() {
+            if cell == 'A' {
+                let rays = _raycast_2((y, x), rows, cols).into_iter().map(|(y, x)| (data[y][x], (y, x))).collect_vec();
+                let ms = rays.iter().filter(|(c, _)| *c == 'M').collect_vec();
+                if ms.len() == 2 &&
+                    rays.iter().filter(|(c, _)| *c == 'S').count() == 2 &&
+                    (ms[0].1.0 == ms[1].1.0 || ms[0].1.1 == ms[1].1.1) {
+                        count += 1;
+                }
+            }
+        }
+    }
+
+    count
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    fn read () -> I {
+        let data = inc!(4);
+        _parse(data)
+    }
+
+    #[test]
+    fn silver () {
+        let data = read();
+        let ans = _silver(data);
+
+        assert_eq!(ans, 2603)
+    }
+
+    #[test]
+    fn gold () {
+        let data = read();
+        let ans = _gold(data);
+
+        assert_eq!(ans, 1965)
+    }
+}