solution: day1

src/bin/01.rs

@@ -0,0 +1,97 @@
+use hashbrown::HashSet;
+
+enum Rotation {
+    Left,
+    Right,
+}
+
+fn rotate(direction: (isize, isize), rotation: &Rotation) -> (isize, isize) {
+    match rotation {
+        Rotation::Right => (-direction.1, direction.0),
+        Rotation::Left => (direction.1, -direction.0),
+    }
+}
+
+enum Direction {
+    Move(isize),
+    Rotate(Rotation),
+}
+
+fn expand_directions(dv: &mut Vec<Direction>, d: &str) {
+    let (r, m) = d.split_at(1);
+
+    let dir = match r {
+        "L" => Rotation::Left,
+        "R" => Rotation::Right,
+        _ => unreachable!(),
+    };
+
+    dv.push(Direction::Rotate(dir));
+    dv.push(Direction::Move(m.parse().unwrap()));
+}
+
+pub fn part_one(input: &str) -> Option<isize> {
+    let mut directions = Vec::new();
+
+    for d in input.split(", ") {
+        expand_directions(&mut directions, d);
+    }
+
+    let (mut x, mut y) = (0, 0);
+    let (mut dx, mut dy) = (1, 0);
+
+    for d in directions {
+        match d {
+            Direction::Rotate(r) => (dx, dy) = rotate((dx, dy), &r),
+            Direction::Move(n) => (x, y) = (x + dx * n, y + dy * n),
+        }
+    }
+
+    Some(x.abs() + y.abs())
+}
+pub fn part_two(input: &str) -> Option<isize> {
+    let mut directions = Vec::new();
+
+    for d in input.split(", ") {
+        expand_directions(&mut directions, d);
+    }
+
+    let (mut x, mut y) = (0, 0);
+    let (mut dx, mut dy) = (1, 0);
+    let mut visited = HashSet::new();
+
+    for d in directions {
+        match d {
+            Direction::Rotate(r) => (dx, dy) = rotate((dx, dy), &r),
+            Direction::Move(n) => {
+                for _ in 1..=n {
+                    (x, y) = (x + dx, y + dy);
+                    if !visited.insert((x, y)) {
+                        return Some(x.abs() + y.abs());
+                    }
+                }
+            }
+        }
+    }
+
+    None
+}
+fn main() {
+    let input = &aoc::read_file("inputs", 1);
+    aoc::solve!(1, part_one, input);
+    aoc::solve!(2, part_two, input);
+}
+#[cfg(test)]
+mod tests {
+    use super::*;
+    #[test]
+    fn test_part_one() {
+        let input = aoc::read_file("examples", 1);
+        assert_eq!(part_one(&input), Some(8));
+    }
+    #[test]
+    fn test_part_two() {
+        let input = aoc::read_file("examples", 1);
+        assert_eq!(part_two(&input), Some(4));
+    }
+}

src/examples/01.txt

@@ -0,0 +1 @@
+R8, R4, R4, R8