[rs] Solve 2022_09 part 1

rs/src/y2022/d09.rs

@@ -0,0 +1,60 @@
+use std::collections::HashSet;
+
+#[derive(Clone, Copy, PartialEq, Eq)]
+enum Direction {
+    Left,
+    Right,
+    Down,
+    Up,
+}
+
+impl Direction {
+    fn from_str(s: &str) -> Option<Self> {
+        match s {
+            "L" => Some(Self::Left),
+            "R" => Some(Self::Right),
+            "D" => Some(Self::Down),
+            "U" => Some(Self::Up),
+            _ => None,
+        }
+    }
+
+    fn move_head(self, head: (i32, i32)) -> (i32, i32) {
+        match self {
+            Self::Left => (head.0 - 1, head.1),
+            Self::Right => (head.0 + 1, head.1),
+            Self::Down => (head.0, head.1 - 1),
+            Self::Up => (head.0, head.1 + 1),
+        }
+    }
+
+    fn move_tail(self, anchor: (i32, i32), tail: (i32, i32)) -> (i32, i32) {
+        match self {
+            Self::Left if tail.0 > anchor.0 + 1 => (anchor.0 + 1, anchor.1),
+            Self::Right if tail.0 < anchor.0 - 1 => (anchor.0 - 1, anchor.1),
+            Self::Down if tail.1 > anchor.1 + 1 => (anchor.0, anchor.1 + 1),
+            Self::Up if tail.1 < anchor.1 - 1 => (anchor.0, anchor.1 - 1),
+            _ => tail,
+        }
+    }
+}
+
+pub fn solve(input: String) {
+    // +x points right, +y points up
+    let mut head = (0, 0);
+    let mut tail = (0, 0);
+    let mut tail_trail = HashSet::new();
+
+    for line in input.lines() {
+        let (dir, amount) = line.split_once(' ').unwrap();
+        let dir = Direction::from_str(dir).unwrap();
+        let amount = amount.parse::<i32>().unwrap();
+        for _ in 0..amount {
+            head = dir.move_head(head);
+            tail = dir.move_tail(head, tail);
+            tail_trail.insert(tail);
+        }
+    }
+
+    println!("Part 1: {}", tail_trail.len());
+}