solution: day2

src/bin/02.rs

@@ -0,0 +1,79 @@
+use hashbrown::HashMap;
+use itertools::Itertools;
+
+fn direction(d: char) -> (isize, isize) {
+    match d {
+        'U' => (-1, 0),
+        'D' => (1, 0),
+        'L' => (0, -1),
+        'R' => (0, 1),
+        _ => unreachable!(),
+    }
+}
+
+pub fn part_one(input: &str) -> Option<isize> {
+    let (mut y, mut x) = (1, 1);
+    let digits: HashMap<(isize, isize), isize> = (0..=2)
+        .cartesian_product(0..=2)
+        .map(|(y, x)| ((y, x), y * 3 + x + 1))
+        .collect();
+
+    let mut res = 0;
+
+    for line in input.lines() {
+        res *= 10;
+        for c in line.chars() {
+            let (dy, dx) = direction(c);
+            let (ny, nx) = (y + dy, x + dx);
+            if digits.contains_key(&(ny, nx)) {
+                (y, x) = (ny, nx);
+            }
+        }
+        res += digits[&(y, x)];
+    }
+
+    Some(res)
+}
+pub fn part_two(input: &str) -> Option<String> {
+    let (mut y, mut x) = (2, 0);
+    #[rustfmt::skip]
+    let digits = HashMap::<(isize, isize), char>::from([
+        ((0, 2), '1'), ((1, 1), '2'), ((1, 2), '3'), ((1, 3), '4'),
+        ((2, 0), '5'), ((2, 1), '6'), ((2, 2), '7'), ((2, 3), '8'),
+        ((2, 4), '9'), ((3, 1), 'A'), ((3, 2), 'B'), ((3, 3), 'C'),
+        ((4, 2), 'D'),
+    ]);
+    let mut res = String::new();
+
+    for line in input.lines() {
+        for c in line.chars() {
+            let (dy, dx) = direction(c);
+            let (ny, nx) = (y + dy, x + dx);
+            if digits.contains_key(&(ny, nx)) {
+                (y, x) = (ny, nx);
+            }
+        }
+        res.push(digits[&(y, x)]);
+    }
+
+    Some(res)
+}
+fn main() {
+    let input = &aoc::read_file("inputs", 2);
+    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", 2);
+        assert_eq!(part_one(&input), Some(1985));
+    }
+    #[test]
+    fn test_part_two() {
+        let input = aoc::read_file("examples", 2);
+        assert_eq!(part_two(&input), Some("5DB3".to_string()));
+    }
+}

src/examples/02.txt

@@ -0,0 +1,4 @@
+ULL
+RRDDD
+LURDL
+UUUUD