advent-of-code-2023/src/day16.rs

use std::io;

#[derive(PartialEq)]
enum Dir {
  North,
  South,
  East,
  West,
}

fn visit(board: &Vec<Vec<char>>, x: i64, y: i64, dir: Dir, visited: &mut Vec<Vec<(bool, bool)>>) {
  if x < 0 || x >= board.len() as i64 {
    return;
  }
  if y < 0 || y >= board[x as usize].len() as i64 {
    return;
  }
  match board[x as usize][y as usize] {
    '.' => match dir {
      Dir::North | Dir::South => {
        if visited[x as usize][y as usize].0 {
          return;
        }
        visited[x as usize][y as usize].0 = true;
        if dir == Dir::North {
          visit(board, x - 1, y, dir, visited);
        } else {
          visit(board, x + 1, y, dir, visited);
        }
      }
      Dir::West | Dir::East => {
        if visited[x as usize][y as usize].1 {
          return;
        }
        visited[x as usize][y as usize].1 = true;
        if dir == Dir::West {
          visit(board, x, y - 1, dir, visited);
        } else {
          visit(board, x, y + 1, dir, visited);
        }
      }
    },
    '\\' => {
      visited[x as usize][y as usize].0 = true;
      match dir {
        Dir::North => visit(board, x, y - 1, Dir::West, visited),
        Dir::South => visit(board, x, y + 1, Dir::East, visited),
        Dir::West => visit(board, x - 1, y, Dir::North, visited),
        Dir::East => visit(board, x + 1, y, Dir::South, visited),
      }
    }
    '/' => {
      visited[x as usize][y as usize].0 = true;
      match dir {
        Dir::North => visit(board, x, y + 1, Dir::East, visited),
        Dir::South => visit(board, x, y - 1, Dir::West, visited),
        Dir::West => visit(board, x + 1, y, Dir::South, visited),
        Dir::East => visit(board, x - 1, y, Dir::North, visited),
      }
    }
    '|' => {
      visited[x as usize][y as usize].0 = true;
      match dir {
        Dir::North => visit(board, x - 1, y, Dir::North, visited),
        Dir::South => visit(board, x + 1, y, Dir::South, visited),
        Dir::West | Dir::East => {
          visit(board, x + 1, y, Dir::South, visited);
          visit(board, x - 1, y, Dir::North, visited);
        }
      }
    }
    '-' => {
      visited[x as usize][y as usize].0 = true;
      match dir {
        Dir::North | Dir::South => {
          visit(board, x, y + 1, Dir::East, visited);
          visit(board, x, y - 1, Dir::West, visited);
        }
        Dir::West => visit(board, x, y - 1, Dir::West, visited),
        Dir::East => visit(board, x, y + 1, Dir::East, visited),
      }
    }
    c => panic!("Unhandled character {}", c),
  }
}

fn count_energized(board: &Vec<Vec<char>>, locx: i64, locy: i64, dir: Dir) -> usize {
  let mut visited = Vec::new();
  for _ in 0..board.len() {
    visited.push(vec![(false, false); board[0].len()]);
  }

  visit(board, locx, locy, dir, &mut visited);
  visited
    .iter()
    .fold(0, |acc, v| acc + v.iter().filter(|(a, b)| *a || *b).count())
}

pub fn solve() -> usize {
  let mut buffer = String::new();

  while io::stdin().read_line(&mut buffer).unwrap() > 0 {}

  count_energized(
    &buffer
      .trim()
      .split("\n")
      .map(|s| s.chars().collect())
      .collect(),
    0,
    0,
    Dir::East,
  )
}

fn best_case(board: &Vec<Vec<char>>) -> usize {
  let mut best = 0;
  for r in 0..board.len() {
    best = best.max(count_energized(board, r as i64, 0, Dir::East));
    best = best.max(count_energized(
      board,
      r as i64,
      (board[r].len() - 1) as i64,
      Dir::West,
    ));
  }

  for c in 0..board[0].len() {
    best = best.max(count_energized(board, 0, c as i64, Dir::South));
    best = best.max(count_energized(
      board,
      (board.len() - 1) as i64,
      c as i64,
      Dir::North,
    ));
  }
  best
}

pub fn find_best() -> usize {
  let mut buffer = String::new();

  while io::stdin().read_line(&mut buffer).unwrap() > 0 {}
  let board = buffer
    .trim()
    .split("\n")
    .map(|s| s.chars().collect())
    .collect();
  best_case(&board)
}