1 files changed, 149 insertions, 0 deletions
diff --git a/aoc22/day9/src/main.rs b/aoc22/day9/src/main.rs
new file mode 100644
index 0000000..f1043f7
--- /dev/null
+++ b/aoc22/day9/src/main.rs
@@ -0,0 +1,149 @@
+use std::collections::HashSet;
+
+fn main() {
+    let input = lib::read_input(9);
+
+    part1(&input);
+    part2(&input);
+}
+
+type P = [i32; 2];
+
+fn part1(input: &str) {
+    let mut visited = HashSet::new();
+
+    let mut head = [0, 0];
+    let mut tail = [0, 0];
+    visited.insert(tail);
+
+    for line in input.lines() {
+        let (dir, dist) = line.split_at(1);
+        let dist = dist[1..].parse::<i32>().unwrap();
+
+        let d = match dir {
+            "L" => [-1, 0],
+            "U" => [0, -1],
+            "D" => [0, 1],
+            "R" => [1, 0],
+            _ => panic!("invalid direction"),
+        };
+
+        for _ in 0..dist {
+            head[0] += d[0];
+            head[1] += d[1];
+
+            if distance(tail, head) <= 1 {
+                continue;
+            }
+
+            let m = len1(tail, head);
+
+            tail[0] += m[0];
+            tail[1] += m[1];
+
+            visited.insert(tail);
+        }
+    }
+    println!("{}", visited.len());
+}
+
+fn part2(input: &str) {
+    let mut visited = HashSet::new();
+
+    let mut rope = [[0, 0]; 10];
+    visited.insert(rope[9]);
+
+    for line in input.lines() {
+        let (dir, dist) = line.split_at(1);
+        let dist = dist[1..].parse::<i32>().unwrap();
+
+        let d = match dir {
+            "L" => [-1, 0],
+            "U" => [0, -1],
+            "D" => [0, 1],
+            "R" => [1, 0],
+            _ => panic!("invalid direction"),
+        };
+
+        for _ in 0..dist {
+            rope[0][0] += d[0];
+            rope[0][1] += d[1];
+
+            for i in 1..rope.len() {
+                if distance(rope[i], rope[i - 1]) <= 1 {
+                    break;
+                }
+
+                let m = len1(rope[i], rope[i - 1]);
+
+                rope[i][0] += m[0];
+                rope[i][1] += m[1];
+
+                if i == rope.len() - 1 {
+                    visited.insert(rope[i]);
+                }
+            }
+        }
+
+        // print(&visited, &rope);
+    }
+    println!("{}", visited.len());
+}
+
+fn distance(a: P, b: P) -> i32 {
+    (a[0] - b[0]).abs().max((a[1] - b[1]).abs())
+}
+
+fn len1(from: P, to: P) -> P {
+    [
+        (to[0] - from[0]).clamp(-1, 1),
+        (to[1] - from[1]).clamp(-1, 1),
+    ]
+}
+
+fn print(visited: &HashSet<P>, rope: &[P]) {
+    let x_min = *visited
+        .iter()
+        .map(|[x, _]| x)
+        .min()
+        .unwrap()
+        .min(rope.iter().map(|[x, _]| x).min().unwrap());
+    let x_max = *visited
+        .iter()
+        .map(|[x, _]| x)
+        .max()
+        .unwrap()
+        .max(rope.iter().map(|[x, _]| x).max().unwrap());
+    let y_min = *visited
+        .iter()
+        .map(|[_, y]| y)
+        .min()
+        .unwrap()
+        .min(rope.iter().map(|[_, y]| y).min().unwrap());
+    let y_max = *visited
+        .iter()
+        .map(|[_, y]| y)
+        .max()
+        .unwrap()
+        .max(rope.iter().map(|[_, y]| y).max().unwrap());
+
+    for y in y_min..=y_max {
+        for x in x_min..=x_max {
+            if x == 0 && y == 0 {
+                eprint!("\x1b[31m");
+            }
+            if [x, y] == rope[0] {
+                eprint!("H");
+            } else if let Some((i, _)) = rope.iter().enumerate().find(|(i, &b)| b == [x, y]) {
+                eprint!("{}", i);
+            } else if visited.contains(&[x, y]) {
+                eprint!("#");
+            } else {
+                eprint!(".");
+            }
+            eprint!("\x1b[0m");
+        }
+        eprintln!();
+    }
+    eprintln!();
+}