day 09.

Cargo.lock

@@ -65,6 +65,8 @@ name = "day09"
 version = "0.1.0"
 dependencies = [
  "aoc_libs",
+ "once_cell",
+ "regex",
 ]
 
 [[package]]

days/day09/Cargo.toml

@@ -7,3 +7,5 @@ edition.workspace = true
 
 [dependencies]
 aoc_libs.workspace = true
+regex.workspace = true
+once_cell.workspace = true

days/day09/src/main.rs

@@ -12,6 +12,6 @@ fn main() {
     println!("Part One");
     println!("Result: {}", part1::part1(&structured_input));
 
-    // println!("Part Two");
-    // println!("Result: {}", part2::part2(&structured_input));
+    println!("Part Two");
+    println!("Result: {}", part2::part2(&structured_input));
 }

days/day09/src/parse.rs

@@ -1,3 +1,6 @@
+use once_cell::sync::Lazy;
+use regex::Regex;
+
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub enum Direction {
     Up,
@@ -6,18 +9,25 @@ pub enum Direction {
     Left,
 }
 
+static PARSE_REGEX: Lazy<Regex> = Lazy::new(|| Regex::new(r"^([URDL]) (\d+)$").unwrap());
+
 pub fn parse(input: &str) -> Vec<Direction> {
     let mut ret = Vec::new();
     for line in input.lines() {
-        let mut chars = line.chars();
-        let dir = match chars.next().unwrap() {
-            'U' => Direction::Up,
-            'R' => Direction::Right,
-            'D' => Direction::Down,
-            'L' => Direction::Left,
+        let captures = PARSE_REGEX
+            .captures(line)
+            .unwrap_or_else(|| panic!("invalid line {}", line));
+        let dir = match &captures[1] {
+            "U" => Direction::Up,
+            "R" => Direction::Right,
+            "D" => Direction::Down,
+            "L" => Direction::Left,
             _ => panic!("invalid direction char"),
         };
-        for _ in 0..chars.nth(1).unwrap().to_digit(10).unwrap() {
+        for _ in 0..captures[2]
+            .parse()
+            .unwrap_or_else(|_| panic!("invalid line {}", line))
+        {
             ret.push(dir)
         }
     }

days/day09/src/part2.rs

@@ -2,25 +2,30 @@ use std::collections::HashSet;
 
 use aoc_libs::points::Point;
 
-use crate::{rope::Rope, parse::Direction};
+use crate::{parse::Direction, rope::Rope};
 
 pub fn part2(input: &Vec<Direction>) -> usize {
     let mut visited: HashSet<Point> = HashSet::new();
     let mut rope: Rope<10> = Rope::new();
+    visited.insert(*rope.get_tail_pos());
     for direction in input {
-        visited.insert(*rope.get_tail_pos());
         rope.update_rope(direction);
-        println!("{}", rope)
+        visited.insert(*rope.get_tail_pos());
     }
     visited.len()
 }
 
 #[cfg(test)]
 mod tests {
+    use crate::parse::parse;
+
     use super::*;
 
     #[test]
     fn test_part2() {
-        assert_eq!(0, 0);
+        let input = parse(concat!(
+            "R 5\n", "U 8\n", "L 8\n", "D 3\n", "R 17\n", "D 10\n", "L 25\n", "U 20\n",
+        ));
+        assert_eq!(part2(&input), 36);
     }
 }

days/day09/src/rope.rs

@@ -23,14 +23,12 @@ impl<const L: usize> Rope<L> {
             Direction::Down => Point { x: 0, y: -1 },
             Direction::Left => Point { x: -1, y: 0 },
         };
-        println!("direction is {:?}", direction);
         for segment in 1..self.segments.len() {
             self.segments[segment] += Rope::<L>::update_single_segment_pair(
                 &self.segments[segment - 1],
                 &self.segments[segment],
             )
         }
-        println!("{}", self);
     }
 
     pub fn get_tail_pos(&self) -> &Point {
@@ -77,7 +75,7 @@ impl<const L: usize> Display for Rope<{ L }> {
         }
 
         for segment in self.segments.iter().skip(1) {
-            let delta =  *segment-self.segments[0];
+            let delta = *segment - self.segments[0];
             let upoint = delta.to_upoint(&zero_point).unwrap();
             grid[upoint.y][upoint.x] = 'T'
         }
@@ -138,9 +136,11 @@ mod tests {
         let mut visited: HashSet<Point> = HashSet::new();
         let mut rope: Rope<2> = Rope::new();
         visited.insert(*rope.get_tail_pos());
+        println!("{}", rope);
         for direction in input {
             rope.update_rope(&direction);
             visited.insert(*rope.get_tail_pos());
+            println!("{}", rope);
         }
         // let mut graph = [
         //     ['.', '.', '.', '.', '.', '.'],