diff --git a/src/day7.rs b/src/day7.rs
index ff15339..f459c4b 100644
--- a/src/day7.rs
+++ b/src/day7.rs
@@ -1,16 +1,39 @@
+use std::collections::HashSet;
+use std::str::FromStr;
+
 use aoc_runner_derive::{aoc, aoc_generator};
+use grid::{AsCoord2d, Grid};
+
 #[aoc_generator(day7)]
-fn parse(input: &str) -> String {
-    todo!()
+fn parse(input: &str) -> Grid<u8> {
+    Grid::from_str(input).unwrap()
+}
+
+//
+fn emit_beams(grid: &mut Grid<u8>, pos: impl AsCoord2d) -> u64 {
+    match grid.get(&pos) {
+        None | Some(b'|') => 0,
+        Some(b'.') | Some(b'S') => {
+            grid.set(&pos, b'|');
+            emit_beams(grid, &(pos.x(), pos.y() + 1))
+        }
+        Some(b'^') => {
+            grid.set(&pos, b'|');
+            1 + emit_beams(grid, &(pos.x() - 1, pos.y()))
+                + emit_beams(grid, &(pos.x() + 1, pos.y()))
+        }
+        _ => panic!(),
+    }
 }
 
 #[aoc(day7, part1)]
-fn part1(input: &str) -> u64 {
-    0
+fn part1(input: &Grid<u8>) -> u64 {
+    let mut grid = input.clone();
+    emit_beams(&mut grid, input.find(&b'S').unwrap())
 }
 
 #[aoc(day7, part2)]
-fn part2(input: &str) -> u64 {
+fn part2(input: &Grid<u8>) -> u64 {
     0
 }
 
@@ -18,11 +41,26 @@ fn part2(input: &str) -> u64 {
 mod tests {
     use super::*;
 
-    const EXAMPLE: &str = "";
+    const EXAMPLE: &str = ".......S.......
+...............
+.......^.......
+...............
+......^.^......
+...............
+.....^.^.^.....
+...............
+....^.^...^....
+...............
+...^.^...^.^...
+...............
+..^...^.....^..
+...............
+.^.^.^.^.^...^.
+...............";
 
     #[test]
     fn part1_example() {
-        assert_eq!(part1(&parse(EXAMPLE)), 0);
+        assert_eq!(part1(&parse(EXAMPLE)), 21);
     }
 
     #[test]