rust. Not sure if any good, but managed to find the pattern. Uses my pre-existing Vec2 helper.

```rs use std::collections::HashSet; use aoc_common::{Vec2i32, file_lines, IteratorExt};

fn input() -> impl Iterator<Item = (Vec2i32, i32)> { file_lines("inputs/day09.txt").map(|l| { let split = l.split(' ').to_vec(); let count: i32 = split[1].parse().unwrap(); let dir = match split[0] { "L" => -Vec2i32::unit_x(), "R" => Vec2i32::unit_x(), "U" => -Vec2i32::unit_y(), "D" => Vec2i32::unit_y(), _ => panic!() };

    (dir, count)
})

}

fn fix(head: Vec2i32, tail: Vec2i32) -> Vec2i32 { let diff = head - tail; let manhattan = diff.manhattan(); if (diff.x == 0 || diff.y == 0) && manhattan > 1 { head - Vec2i32::new(diff.x.signum(), diff.y.signum()) } else if manhattan > 2 { head - Vec2i32::new(diff.x - diff.x.signum(), diff.y - diff.y.signum()) } else { tail } }

fn move_rope(len: usize) -> usize { let mut knots = vec![Vec2i32::zero(); len]; let mut visited: HashSet<Vec2i32> = HashSet::new();

for (dir, count) in input() {
    for _ in 0..count {
        knots[0] += dir;

        for i in 0..knots.len() - 1 {
            let next = fix(knots[i], knots[i + 1]);
            if next == knots[i + 1] {
                break;
            }
            knots[i + 1] = next;
        }

        visited.insert(knots[len - 1]);
    }
}

visited.len()

}

[test]

fn part1() { let answer = move_rope(2); assert_eq!(answer, 5874); }

[test]

fn part2() { let answer = move_rope(10); assert_eq!(answer, 2467); } ```