From dc0c839f0c256a6c2f5e7702042bba9e54b2a9c8 Mon Sep 17 00:00:00 2001
From: alex <>
Date: Sun, 7 Dec 2025 20:02:27 +0100
Subject: [PATCH] day07: part1

---
 src/day07.rs | 84 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 src/main.rs  |  2 ++
 2 files changed, 86 insertions(+)
 create mode 100644 src/day07.rs

diff --git a/src/day07.rs b/src/day07.rs
new file mode 100644
index 0000000..6d10e24
--- /dev/null
+++ b/src/day07.rs
@@ -0,0 +1,84 @@
+use std::error::Error;
+use std::collections::HashMap;
+
+struct Puzzle {
+    start: (usize, usize),
+    map: HashMap<(usize, usize), (char, bool)>, // bool to store if key has been visited already
+}
+
+impl Puzzle {
+    fn new(input: &str) -> Self {
+        let mut start = (0, 0);
+        let mut map = HashMap::new();
+        input.lines().enumerate()
+            .for_each(|(i, l)| {
+                l.chars().enumerate()
+                    .for_each(|(j, c)| {
+                        if c == 'S' {
+                            start = (i, j);
+                        }
+                        map.insert((i, j), (c, false)); });
+            });
+        Puzzle { start, map }
+    }
+
+    fn part1(&mut self) -> u64 {
+        let mut splitters = 0;
+        let mut beam: Vec<(usize, usize)> = Vec::new();
+        beam.push((self.start.0 + 1, self.start.1));
+        while let Some(pos) = beam.pop() {
+            if self.map.contains_key(&pos) {
+                let mut location = self.map.get_mut(&pos).unwrap();
+                if location.1 {
+                    continue;
+                }
+                location.1 = true;
+                match location.0 {
+                    '.' => { beam.push((pos.0 + 1, pos.1)); },
+                    '^' => {
+                        splitters += 1;
+                        beam.push((pos.0, pos.1 - 1));
+                        beam.push((pos.0, pos.1 + 1));
+                    },
+                    _ => {},
+                }
+            }
+        }
+        splitters
+    }
+}
+
+pub fn run(input: &str) -> Result<(), Box<dyn Error>> {
+    let mut p = Puzzle::new(input);
+    println!("part1: {}", p.part1());
+    Ok(())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    static TEST_INPUT: &str = "\
+.......S.......
+...............
+.......^.......
+...............
+......^.^......
+...............
+.....^.^.^.....
+...............
+....^.^...^....
+...............
+...^.^...^.^...
+...............
+..^...^.....^..
+...............
+.^.^.^.^.^...^.
+...............
+";
+
+    #[test]
+    fn test_part1() {
+        assert_eq!(21, Puzzle::new(TEST_INPUT).part1());
+    }
+}
diff --git a/src/main.rs b/src/main.rs
index 1d043c3..8cb86b2 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -10,6 +10,7 @@ pub mod day03;
 pub mod day04;
 pub mod day05;
 pub mod day06;
+pub mod day07;
 
 fn main() {
     let args: Vec<String> = env::args().collect();
@@ -31,6 +32,7 @@ fn run(day: &str, input_file: &str) -> Result<(), Box<dyn Error>> {
         "day04" => day04::run(&input)?,
         "day05" => day05::run(&input)?,
         "day06" => day06::run(&input)?,
+        "day07" => day07::run(&input)?,
         _ => return Err(format!("unknown or unimplemented day \"{day}\"").into()),
     }
     Ok(())
-- 
2.39.5