Scala3

forgot to post this

import Area.*
import Dir.*

enum Dir(num: Int, diff: (Int, Int)):
    val n = num
    val d = diff
    case Up extends Dir(3, (0, -1))
    case Down extends Dir(1, (0, 1))
    case Left extends Dir(2, (-1, 0))
    case Right extends Dir(0, (1, 0))
    def opposite = Dir.from(n + 2)

object Dir:
    def from(n: Int): Dir = Dir.all.filter(_.n == n % 4).ensuring(_.size == 1).head
    def all = List(Up, Down, Left, Right)

enum Area:
    case Inside, Outside, Loop

case class Pos(x: Int, y: Int)
type Landscape = Map[Pos, Pipe]
type Loop = Map[Pos, LoopPiece]

def walk(p: Pos, d: Dir): Pos = Pos(p.x + d.d._1, p.y + d.d._2)

val pipeMap = Map('|' -> List(Up, Down), '-' -> List(Left, Right), 'L' -> List(Up, Right), 'J' -> List(Up, Left), 'F' -> List(Right, Down), '7' -> List(Left, Down))

case class Pipe(neighbors: List[Dir])
case class LoopPiece(from: Dir, to: Dir):
    def left: List[Dir] = ((from.n + 1) until (if to.n < from.n then to.n + 4 else to.n)).map(Dir.from).toList
    def right: List[Dir] = LoopPiece(to, from).left

def parse(a: List[String]): (Pos, Landscape) =
    val pipes = for (r, y) <- a.zipWithIndex; (v, x) <- r.zipWithIndex; p <- pipeMap.get(v) yield Pos(x, y) -> Pipe(p) 
    val start = for (r, y) <- a.zipWithIndex; (v, x) <- r.zipWithIndex if v == 'S' yield Pos(x, y)
    (start.head, pipes.toMap)

def walkLoop(start: Pos, l: Landscape): Loop =
    @tailrec def go(pos: Pos, last_dir: Dir, acc: Loop): Loop =
        if pos == start then acc else
            val dir = l(pos).neighbors.filter(_ != last_dir.opposite).ensuring(_.size == 1).head
            go(walk(pos, dir), dir, acc + (pos -> LoopPiece(last_dir.opposite, dir)))

    Dir.all.filter(d => l.get(walk(start, d)).exists(p => p.neighbors.contains(d.opposite))) match
        case List(start_dir, return_dir) => go(walk(start, start_dir), start_dir, Map(start -> LoopPiece(return_dir, start_dir)))
        case _ => Map()

def task1(a: List[String]): Long =
    walkLoop.tupled(parse(a)).size.ensuring(_ % 2 == 0) / 2

def task2(a: List[String]): Long =
    val loop = walkLoop.tupled(parse(a))

    val ys = a.indices
    val xs = a.head.indices
    val points = (for x <- xs; y <- ys yield Pos(x, y)).toSet
    
    // floodfill
    @tailrec def go(outside: Set[Pos], q: List[Pos]): Set[Pos] =
        if q.isEmpty then outside else
            val nbs = Dir.all.map(walk(q.head, _)).filter(points.contains(_)).filter(!outside.contains(_))
            go(outside ++ nbs, nbs ++ q.tail)

    // start by floodfilling from the known outside: beyond the array bounds
    val boundary = ys.flatMap(y => List(Pos(-1, y), Pos(xs.end, y))) ++ xs.flatMap(x => List(Pos(x, -1), Pos(x, ys.end)))
    val r = go(boundary.toSet ++ loop.keySet, boundary.toList)

    // check on which side of the pipe the outside is, then continue floodfill from there
    val xsl = List[LoopPiece => List[Dir]](_.left, _.right).map(side => loop.flatMap((p, l) => side(l).map(d => walk(p, d))).filter(!loop.contains(_)).toSet).map(a => a -> a.intersect(r).size).ensuring(_.exists(_._2 == 0)).filter(_._2 != 0).head._1
    (points -- go(r ++ xsl, xsl.toList)).size

Python

Also on Github.

from .solver import Solver

_EXITS_MAP = {
  '|': ((0, -1), (0, 1)),
  '-': ((-1, 0), (1, 0)),
  'L': ((1, 0), (0, -1)),
  'J': ((-1, 0), (0, -1)),
  '7': ((-1, 0), (0, 1)),
  'F': ((1, 0), (0, 1)),
  '.': (),
  'S': (),
}

class Day10(Solver):

  def __init__(self):
    super().__init__(10)
    self.maze: dict[tuple[int, int], str] = {}
    self.start: tuple[int, int] = (0, 0)
    self.dists: dict[tuple[int, int], int] = {}

  def _pipe_has_exit(self, x: int, y: int, di: int, dj: int, inverse: bool = False) -> bool:
    if inverse:
      di, dj = -di, -dj
    return (di, dj) in _EXITS_MAP[self.maze[(x, y)]]

  def presolve(self, input: str):
    self.maze: dict[tuple[int, int], str] = {}
    self.start: tuple[int, int] = (0, 0)
    for y, line in enumerate(input.rstrip().split('\n')):
      for x, c in enumerate(line):
        self.maze[(x, y)] = c
        if c == 'S':
          self.start = (x, y)
    next_pos: list[tuple[int, int]] = []
    directions_from_start = []
    for di, dj in ((0, -1), (1, 0), (0, 1), (-1, 0)):
      x, y = self.start[0] + di, self.start[1] + dj
      if (x, y) not in self.maze:
        continue
      if not self._pipe_has_exit(x, y, di, dj, inverse=True):
        continue
      next_pos.append((x, y))
      directions_from_start.append((di, dj))
    self.maze[self.start] = [c for c, dmap in _EXITS_MAP.items()
                              if set(directions_from_start) == set(dmap)][0]
    dists: dict[tuple[int, int], int] = {}
    cur_dist = 0
    while True:
      cur_dist += 1
      new_next_pos = []
      for x, y in next_pos:
        if (x, y) in dists:
          continue
        dists[(x, y)] = cur_dist
        for di, dj in ((0, -1), (1, 0), (0, 1), (-1, 0)):
          nx, ny = x + di, y + dj
          if (nx, ny) not in self.maze:
            continue
          if not self._pipe_has_exit(x, y, di, dj):
            continue
          new_next_pos.append((nx, ny))
      if not new_next_pos:
        break
      next_pos = new_next_pos
    self.dists = dists

  def solve_first_star(self) -> int:
    return max(self.dists.values())

  def solve_second_star(self) -> int:
    area = 0
    for y in range(max(y for _, y in self.dists.keys()) + 1):
      internal = False
      previous_wall = False
      wall_start_symbol = None
      for x in range(max(x for x, _ in self.dists.keys()) + 1):
        is_wall = (x, y) == self.start or (x, y) in self.dists
        wall_continues = is_wall
        pipe_type = self.maze[(x, y)]
        if is_wall and pipe_type == '|':
          internal = not internal
          wall_continues = False
        elif is_wall and not previous_wall and pipe_type in 'FL':
          wall_start_symbol = pipe_type
        elif is_wall and not previous_wall:
          raise RuntimeError(f'expecting wall F or L at {x}, {y}, got {pipe_type}')
        elif is_wall and previous_wall and pipe_type == 'J':
          wall_continues = False
          if wall_start_symbol == 'F':
            internal = not internal
        elif is_wall and previous_wall and pipe_type == '7':
          wall_continues = False
          if wall_start_symbol == 'L':
            internal = not internal
        elif not is_wall and previous_wall:
          raise RuntimeError(f'expecting wall J or 7 at {x}, {y}, got {pipe_type}')
        if internal and not is_wall:
          area += 1
        previous_wall = wall_continues
    return area

Well, star one is solved. I don't love the code, but yet again, it works for now. I don't love the use of a label to continue/break a loop, and the valid_steps function is a mess that could probably be done much cleaner.

Upon looking at star 2 I don't even have the slightest idea of where to start. I may have to come back to this one at a later date. Sigh.

https://github.com/capitalpb/advent_of_code_2023/blob/main/src/solvers/day10.rs

use crate::Solver;

#[derive(Debug)]
struct PipeMap {
    start: usize,
    tiles: Vec,
    width: usize,
}

impl PipeMap {
    fn from(input: &str) -> PipeMap {
        let tiles = input
            .lines()
            .rev()
            .flat_map(|row| row.chars())
            .collect::>();

        let width = input.find('\n').unwrap();
        let start = tiles.iter().position(|tile| tile == &'S').unwrap();

        PipeMap {
            start,
            tiles,
            width,
        }
    }

    fn valid_steps(&self, index: usize) -> Vec {
        let mut tiles = vec![];
        let current_tile = *self.tiles.get(index).unwrap();

        if "S|LJ".contains(current_tile) {
            let north = index + self.width;
            if let Some(tile) = self.tiles.get(north) {
                if "|7F".contains(*tile) {
                    tiles.push(north);
                }
            }
        }

        if "S|7F".contains(current_tile) {
            if let Some(south) = index.checked_sub(self.width) {
                if let Some(tile) = self.tiles.get(south) {
                    if "|LJ".contains(*tile) {
                        tiles.push(south);
                    }
                }
            }
        }

        if "S-J7".contains(current_tile) {
            if let Some(west) = index.checked_sub(1) {
                if (west % self.width) != (self.width - 1) {
                    if let Some(tile) = self.tiles.get(west) {
                        if "-LF".contains(*tile) {
                            tiles.push(west);
                        }
                    }
                }
            }
        }

        if "S-LF".contains(current_tile) {
            let east = index + 1;
            if east % self.width != 0 {
                if let Some(tile) = self.tiles.get(east) {
                    if "-J7".contains(*tile) {
                        tiles.push(east);
                    }
                }
            }
        }

        tiles
    }
}

pub struct Day10;

impl Solver for Day10 {
    fn star_one(&self, input: &str) -> String {
        let pipe_map = PipeMap::from(input);

        let mut current_pos = pipe_map.start;
        let mut last_pos = pipe_map.start;
        let mut steps: usize = 0;

        'outer: loop {
            for pos in pipe_map.valid_steps(current_pos) {
                if pos != last_pos {
                    last_pos = current_pos;
                    current_pos = pos;
                    steps += 1;

                    continue 'outer;
                }
            }
            break;
        }

        steps.div_ceil(2).to_string()
    }

    fn star_two(&self, input: &str) -> String {
        todo!()
    }
}

I always felt I was one fix away from the solution, which was both nice and bad.

Walking the path was fine, and part 2 looked easy until I missed the squeezed pipes. I for some silly reason thought I only had to expand the grid by x2 instead of x3 and had to re-do that. Fill is hyper bad but works for <1 minute.

import re
import math
import argparse
import itertools
from enum import Flag,Enum

class Connection(Flag):
    Empty = 0b0000
    North = 0b0001
    South = 0b0010
    East = 0b01000
    West = 0b10000

def connected_directions(first:Connection,second:Connection) -> bool:
    return bool(((first.value >> 1) & second.value) or
            ((first.value << 1) & second.value))

def opposite_direction(dir:Connection) -> Connection:
    if dir.value & 0b00011:
        return Connection(dir.value ^ 0b00011)
    if dir.value & 0b11000:
        return Connection(dir.value ^ 0b11000)
    return Connection(0)

class PipeElement:
    def __init__(self,symbol:chr) -> None:
        self.symbol = symbol
        self.connection = Connection.Empty
        if symbol in [*'|LJS']:
            self.connection |= Connection.North
        if symbol in [*'|7FS']:
            self.connection |= Connection.South
        if symbol in [*'-LFS']:
            self.connection |= Connection.East
        if symbol in [*'-J7S']:
            self.connection |= Connection.West
        if self.connection == Connection.Empty:
            self.symbol = '.'

    def __repr__(self) -> str:
        return f"Pipe({self.connection})"
    
    def __str__(self) -> str:
        return self.symbol

    def connected_to(self,pipe,direction:Connection) -> bool:
        if not (self.connection & direction):
            return False
        
        if self.connection & direction and pipe.connection & opposite_direction(direction):
            return True
        
        return False
        
class Navigator:
    def __init__(self,list:list,width) -> None:
        self.list = list
        self.width = width

    def at(self,position):
        return self.list[position]
    
    def neighbor(self,position,direction:Connection) -> tuple | None:
        match direction:
            case Connection.North:
                return self.prev_row(position)
            case Connection.South:
                return self.next_row(position)
            case Connection.East:
                return self.next(position)
            case Connection.West:
                return self.prev(position)
        raise Exception(f"Direction not found: {direction}")

    def prev_row(self,position) -> tuple | None:
        p = position - self.width
        if p < 0:
            return None
        return (p,self.list[p])

    def next_row(self,position) -> tuple | None:
        p = position + self.width
        if p >= len(self.list):
            return None
        return (p,self.list[p])
    
    def prev(self,position) -> tuple | None:
        p = position - 1
        if p < 0:
            return None
        return (p,self.list[p])

    def next(self,position) -> tuple | None:
        p = position + 1
        if p >= len(self.list):
            return None
        return (p,self.list[p])
    
    def all_neighbors(self,position) -> list:
        l = list()
        for f in [self.next, self.prev, self.next_row,self.prev_row]:
            t = f(position)
            if t != None:
                l.append(t)
        return l
    
    def find_connected(self,position,exclude=Connection.Empty) -> tuple | None:
        for dir in [Connection.East,Connection.West,Connection.North,Connection.South]:
            if dir == exclude:
                continue

            n = self.neighbor(position,dir)
            if n == None:
                continue

            if self.at(position).connected_to(n[1],dir):
                return (*n,dir)
        return None

class TileType(Enum):
    Inside = 1
    Outside = 0
    Pipe = 2
    PlaceHolder = 3

def pipe_to_tile_expand(pipe:PipeElement) -> list:
    s = str(pipe)
    expansions = {
        '.': '.PP'+ 'PPP' + 'PPP',
        '-': 'PPP'+ '---' + 'PPP',
        '|': 'P|P'+ 'P|P' + 'P|P',
        'F': 'PPP'+ 'PF-' + 'P|P',
        '7': 'PPP'+ '-7P' + 'P|P',
        'J': 'P|P'+ '-JP' + 'PPP',
        'L': 'P|P'+ 'PL-' + 'PPP',
        'S': 'P|P'+ '-S-' + 'P|P'
        }
    l = expansions[s]
    return [pipe_to_tile(x) for x in [*l]]
def pipe_to_tile(pipe:str) -> TileType:
    expansions = {
        '.': TileType.Inside,
        '-': TileType.Pipe,
        '|': TileType.Pipe,
        'F': TileType.Pipe,
        '7': TileType.Pipe,
        'J': TileType.Pipe,
        'L': TileType.Pipe,
        'S': TileType.Pipe,
        'P': TileType.PlaceHolder
        }
    return expansions[pipe]

def chunks(lst, n):
    """Yield successive n-sized chunks from lst."""
    for i in range(0, len(lst), n):
        yield lst[i:i + n]

def print_tiles(tile_list:list,width:int):
    for c in chunks(tile_list,width):
        print("".join([str(t.value) for t in c]))

def print_pipes(tile_list:list,width:int):
    for c in chunks(tile_list,width):
        print("".join([str(t) for t in c]))

def main(line_list:list,part:int):
    width = None

    pipe_list = list()
    tile_list = list()
    start_o = None
    for line in line_list:
        line = line + ' ' # stops east/west joining over new lines
        if width == None:
            width = len(line)
        for c in [*line]:
            o = PipeElement(c)
            pipe_list.append(o)
            tile_list.append(TileType.Inside)
            if c == 'S':
                start_o = o
    #print(pipe_list)
    start_pos = pipe_list.index(start_o)
    start_co = (start_pos // width, start_pos % width)
    print(f"starting index: {start_pos}: {start_co}")

    nav = Navigator(pipe_list,width)

    cur_pos = None
    last_dir = Connection.Empty
    steps = 0
    while cur_pos != start_pos:
        if cur_pos == None:
            cur_pos = start_pos
        
        pipe = nav.find_connected(cur_pos,exclude=opposite_direction(last_dir))
        if pipe == None:
            raise Exception(f"end of pipe at: {cur_pos}, {nav.at(cur_pos)}")
        cur_pos = pipe[0]
        last_dir = pipe[2]
        steps += 1
        #print(f"{cur_pos}->",end="")

        tile_list[cur_pos] = TileType.Pipe
    
    print(f"end: {cur_pos}, steps: {steps}")

    clean_pipe = list()
    for i in range(0,len(pipe_list)):
        if tile_list[i] == TileType.Pipe:
            clean_pipe.append(pipe_list[i])
        else:
            clean_pipe.append(PipeElement('.'))

    print_pipes(clean_pipe,width)
    print(f"part 1: {steps/2}")

    # part 2 outputs
    #print("start tile:")
    #print_tiles(tile_list,width)

    # add outsides to edge of map
    tile_list2 = list()
    #first row
    expanded_width = (width*3)+2
    for i in range(0,expanded_width):
        tile_list2.append(TileType.Outside)
    for row in chunks(clean_pipe, width):
        ## we need to expand this to 2x size tiles
        t_rows = [ list() for x in range(0,3)]
        [ x.append(TileType.Outside) for x in t_rows]
        for r in row:
            parts = pipe_to_tile_expand(r)
            [ t_rows[x].extend( parts[x*3:(x*3)+3] ) for x in range(0,3)]
        [ x.append(TileType.Outside) for x in t_rows]
        [ tile_list2.extend(x) for x in t_rows]
    for i in range(0,expanded_width):
        tile_list2.append(TileType.Outside)

    #print("with o tile:")
    #print_tiles(tile_list2,width+2)

    tilenav = Navigator(tile_list2,expanded_width)
    changes = True
    while changes == True:
        changes = False
        count_in = 0
        
        for i in range(0,len(tile_list2)):
            t = tilenav.at(i)
            if t == TileType.Inside or t == TileType.PlaceHolder:
                n = tilenav.all_neighbors(i)
                if any([x[1] == TileType.Outside for x in n]):
                    tilenav.list[i] = TileType.Outside
                    changes = True
                    continue
                if t == TileType.Inside:
                    count_in += 1

    print("with outside tile:")
    print_tiles(tile_list2,expanded_width)
    print(count_in)

if __name__ == "__main__":
    parser = argparse.ArgumentParser(description="template for aoc solver")
    parser.add_argument("-input",type=str)
    parser.add_argument("-part",type=int)
    args = parser.parse_args()
    filename = args.input
    if filename == None:
        parser.print_help()
        exit(1)
    part = args.part
    file = open(filename,'r')
    main([line.rstrip('\n') for line in file.readlines()],part)
    file.close()

Language: Python

Github

Decided to use a graph to solve (which expanded the size). Part 1 was cycle detection, and part 2 was flooding of the outside.