done with day9 part1

2022-aoc/src/d9.rs

@@ -0,0 +1,64 @@
+use std::collections::HashSet;
+
+use aoc_runner_derive::{aoc as aoc_run, aoc_generator};
+
+type Position = (i32, i32);
+
+#[aoc_generator(day9)]
+fn parse_input(input: &str) -> Vec<Position> {
+    let mut out = Vec::new();
+    let (mut x, mut y) = (0, 0);
+    out.push((x, y));
+    for line in input.lines() {
+        let mut split = line.split_ascii_whitespace();
+        let dir = split.next().unwrap();
+        let num: i32 = split.next().unwrap().parse().unwrap();
+        for _ in 0..num {
+            match dir {
+                "U" => y += 1,
+                "D" => y -= 1,
+                "L" => x -= 1,
+                "R" => x += 1,
+                _ => unreachable!(),
+            }
+            out.push((x, y));
+        }
+    }
+    out
+}
+
+#[aoc_run(day9, part1)]
+fn part1(input: &[Position]) -> usize {
+    let mut tail = (0, 0);
+    let mut set = HashSet::new();
+    set.insert(tail);
+    for mv in input {
+        tail = new_tail(mv, &tail);
+        set.insert(tail);
+    }
+
+    set.len()
+}
+
+#[aoc_run(day9, part2)]
+fn part2(input: &[Position]) -> u32 {
+    0
+}
+
+fn new_tail(head: &Position, tail: &Position) -> Position {
+    let dy = head.1 - tail.1;
+    let dx = head.0 - tail.0;
+    match (dx, dy) {
+        (0, 0) => *tail,
+        (n, m) if (n.abs() == 1) && (m.abs() == 1) => *tail,
+        (n, 0) | (0, n) if n.abs() == 1 => *tail,
+        (_, 2) | (_, -2) if dx.abs() == 1 => (tail.0 + dx, tail.1 + (dy / 2)),
+        (2, y) | (-2, y) if y.abs() == 1 => {
+            let sign = dx / dx.abs();
+            (tail.0 + sign * (dx.abs() - 1), tail.1 + dy)
+        }
+        (n, _) if n.abs() == 2 => (tail.0 + n / 2, tail.1),
+        (_, n) if n.abs() == 2 => (tail.0, tail.1 + n / 2),
+        _ => unreachable!("got {:?}", (dx, dy)),
+    }
+}

2022-aoc/src/lib.rs

@@ -8,5 +8,6 @@ mod d5;
 mod d6;
 mod d7;
 mod d8;
+mod d9;
 
 aoc_lib! { year = 2022 }