Day 18 - Part 2 - WIP

Signed-off-by: Anthony Oteri <anthony.oteri@gmail.com>

day-18/Cargo.toml

@@ -14,6 +14,7 @@ miette = { workspace = true }
 thiserror = { workspace = true }
 dhat = { workspace = true }
 glam = { workspace = true }
+rayon = { workspace = true }
 
 [dev-dependencies]
 divan = { workspace = true }

day-18/src/part2.rs

@@ -1,8 +1,157 @@
+use std::collections::HashSet;
+
 use crate::error::AocError;
+use glam::IVec2;
+use nom::{
+    branch::alt,
+    bytes::complete::{is_a, tag, take_while_m_n},
+    character::complete::{self, digit1, line_ending, space1},
+    combinator::{map, map_res},
+    multi::separated_list1,
+    sequence::tuple,
+    IResult,
+};
+use rayon::prelude::*;
+
+#[derive(Debug, Clone)]
+enum Direction {
+    North,
+    South,
+    East,
+    West,
+}
+
+#[derive(Debug, Clone)]
+struct Instruction {
+    direction: Direction,
+    distance: u32,
+}
+fn parse_distance(input: &str) -> IResult<&str, u32> {
+    map_res(take_while_m_n(5, 5, |c: char| c.is_ascii_hexdigit()), |v| {
+        u32::from_str_radix(v, 16)
+    })(input)
+}
+
+fn parse_line(input: &str) -> IResult<&str, (Direction, u32)> {
+    let (input, _) = alt((
+        map(complete::char('R'), |_| Direction::East),
+        map(complete::char('L'), |_| Direction::West),
+        map(complete::char('U'), |_| Direction::North),
+        map(complete::char('D'), |_| Direction::South),
+    ))(input)?;
+    let (input, _) = space1(input)?;
+    let (input, _) = map(digit1, |s: &str| s.parse::<u32>().unwrap())(input)?;
+    let (input, _) = space1(input)?;
+    let (input, _) = tag("(#")(input)?;
+    let (input, distance) = parse_distance(input)?;
+    let (input, direction) = alt((
+        map(complete::char('0'), |_| Direction::East),
+        map(complete::char('2'), |_| Direction::West),
+        map(complete::char('3'), |_| Direction::North),
+        map(complete::char('1'), |_| Direction::South),
+    ))(input)?;
+    let (input, _) = tag(")")(input)?;
+
+    Ok((input, (direction, distance)))
+}
+
+fn parse(input: &str) -> IResult<&str, Vec<Instruction>> {
+    let (input, lines) = separated_list1(line_ending, parse_line)(input)?;
+
+    Ok((
+        input,
+        lines
+            .iter()
+            .map(|(direction, distance)| Instruction {
+                direction: direction.clone(),
+                distance: *distance,
+            })
+            .collect(),
+    ))
+}
+
+fn normalize(grid: &HashSet<IVec2>) -> HashSet<IVec2> {
+    let min_x = grid.par_iter().map(|v| v.x).min().unwrap();
+    let min_y = grid.par_iter().map(|v| v.y).min().unwrap();
+
+    let origin = IVec2::new(min_x, min_y);
+
+    let mut normalized = HashSet::new();
+    for pos in grid.iter() {
+        normalized.insert(*pos + origin.abs());
+    }
+
+    normalized
+}
+
+fn detect_edges(grid: &HashSet<IVec2>) -> HashSet<IVec2> {
+    let min_x = grid.par_iter().map(|v| v.x).min().unwrap();
+    let min_y = grid.par_iter().map(|v| v.y).min().unwrap();
+    let max_x = grid.par_iter().map(|v| v.x).max().unwrap();
+    let max_y = grid.par_iter().map(|v| v.y).max().unwrap();
+
+    let mut result = grid.clone();
+    for x in min_x..=max_x {
+        let mut is_inside = false;
+        for y in min_y..max_y {
+            if grid.contains(&IVec2::new(x, y)) {
+                is_inside = !is_inside
+            } else if is_inside {
+                result.insert(IVec2::new(x, y));
+            }
+        }
+    }
+
+    result
+}
+
+fn flood_fill(grid: &HashSet<IVec2>) -> u64 {
+    let min_x = grid.iter().map(|v| v.x).min().unwrap();
+    let min_y = grid.iter().map(|v| v.y).min().unwrap();
+    let max_x = grid.iter().map(|v| v.x).max().unwrap();
+    let max_y = grid.iter().map(|v| v.y).max().unwrap();
+
+    let mut grid = detect_edges(&grid);
+
+    let mut sum: u64 = 0;
+    for y in min_y..max_y {
+        let mut is_inside = false;
+        for x in min_x..=max_x {
+            if grid.contains(&IVec2::new(x, y)) && grid.contains(&IVec2::new(x, y + 1)) {
+                is_inside = !is_inside
+            } else if is_inside {
+                sum += 1;
+            }
+        }
+    }
+    sum
+}
 
 #[tracing::instrument]
 pub fn process(input: &str) -> miette::Result<u64, AocError> {
-    Ok(0)
+    let (input, instructions) = parse(input).unwrap();
+
+    debug_assert!(input.is_empty());
+
+    let mut grid: HashSet<IVec2> = HashSet::new();
+    let mut current = IVec2::splat(0);
+    instructions.into_iter().for_each(|instruction| {
+        grid.insert(current);
+        match instruction.direction {
+            Direction::North => current.y += instruction.distance as i32,
+            Direction::South => current.y -= instruction.distance as i32,
+            Direction::East => current.x += instruction.distance as i32,
+            Direction::West => current.x -= instruction.distance as i32,
+        };
+    });
+
+    let normalized = normalize(&grid);
+    let filled = flood_fill(&normalized);
+
+    //#[cfg(test)]
+    //visualize(&filled);
+
+    Ok(normalized.len() as u64)
 }
 
 #[cfg(test)]
@@ -12,7 +161,7 @@ mod tests {
     #[test_log::test]
     fn test_process() -> miette::Result<()> {
         let input = include_str!("../test-input.txt");
-        assert_eq!(0, process(input)?);
+        assert_eq!(952408144115, process(input)?);
         Ok(())
     }
 }