clippy

src/day06.rs

@@ -0,0 +1,137 @@
+use std::{
+    collections::{HashMap, HashSet},
+    fs::read_to_string,
+};
+
+pub fn day_main() {
+    let input = read_to_string("input/day06.txt").unwrap();
+    let input = input.trim();
+    println!(" part1: {}", part1(input));
+    println!(" part2: {}", part2(input));
+}
+
+type RiddleResult = usize;
+type Point = (i32, i32);
+
+fn part1(input: &str) -> RiddleResult {
+    let (m, mut pos, _) = parse(input);
+
+    let mut dir = '^';
+    let mut visited = HashSet::new();
+    while m.contains_key(&pos) {
+        let (x, y) = pos;
+        visited.insert(pos);
+        let next = match dir {
+            '^' => (x, y - 1),
+            'v' => (x, y + 1),
+            '<' => (x - 1, y),
+            '>' => (x + 1, y),
+            _ => unreachable!(),
+        };
+        if let Some('#') = m.get(&next) {
+            dir = match dir {
+                '^' => '>',
+                'v' => '<',
+                '<' => '^',
+                '>' => 'v',
+                _ => unreachable!("asdf"),
+            };
+        } else {
+            pos = next;
+        }
+    }
+    visited.len()
+}
+
+fn part2(input: &str) -> RiddleResult {
+    let (m, pos, opens) = parse(input);
+
+    let dir = '^';
+    opens
+        .into_iter()
+        .filter(|open| {
+            let mut m = m.clone();
+            m.insert(*open, '#');
+            is_loop(m, pos, dir)
+        })
+        .count()
+}
+
+fn parse(input: &str) -> (HashMap<Point, char>, Point, HashSet<Point>) {
+    let mut m = HashMap::new();
+    let mut pos = None;
+    let mut opens = HashSet::new();
+    input.lines().enumerate().for_each(|(y, line)| {
+        line.char_indices().for_each(|(x, c)| {
+            let x = x as i32;
+            let y = y as i32;
+            if c == '^' {
+                pos = Some((x, y));
+                m.insert((x, y), '.');
+            } else {
+                m.insert((x, y), c);
+            }
+            if c == '.' {
+                opens.insert((x, y));
+            }
+        });
+    });
+    (m, pos.unwrap(), opens)
+}
+
+fn is_loop(m: HashMap<Point, char>, mut pos: Point, mut dir: char) -> bool {
+    let mut visited = HashSet::new();
+    while m.contains_key(&pos) {
+        let (x, y) = pos;
+        if visited.contains(&(pos, dir)) {
+            return true;
+        }
+        visited.insert((pos, dir));
+        let next = match dir {
+            '^' => (x, y - 1),
+            'v' => (x, y + 1),
+            '<' => (x - 1, y),
+            '>' => (x + 1, y),
+            _ => unreachable!(),
+        };
+        if let Some('#') = m.get(&next) {
+            dir = match dir {
+                '^' => '>',
+                'v' => '<',
+                '<' => '^',
+                '>' => 'v',
+                _ => unreachable!("asdf"),
+            };
+        } else {
+            pos = next;
+        }
+    }
+    false
+}
+
+#[cfg(test)]
+mod test {
+    use super::{part1, part2};
+
+    const TEST_INPUT: &str = r"....#.....
+.........#
+..........
+..#.......
+.......#..
+..........
+.#..^.....
+........#.
+#.........
+......#...
+";
+
+    #[test]
+    fn test1() {
+        assert_eq!(part1(TEST_INPUT), 41);
+    }
+
+    #[test]
+    fn test2() {
+        assert_eq!(part2(TEST_INPUT), 6);
+    }
+}

src/lib.rs

@@ -3,3 +3,4 @@ pub mod day02;
 pub mod day03;
 pub mod day04;
 pub mod day05;
+pub mod day06;

src/main.rs

@@ -10,6 +10,7 @@ fn main() {
         (3, day03::day_main),
         (4, day04::day_main),
         (5, day05::day_main),
+        (6, day06::day_main),
     ]);
     let day: Option<u8> = args().nth(1).and_then(|a| a.parse().ok());
     let Some(day) = day else {