adventofcode-2019/day03/Day03.rs

use std::{
    error::Error,
    fmt::{self, Formatter, Display},
    io::{self, Read},
    mem,
    str::FromStr,
};

type Result<T> = std::result::Result<T, Box<dyn Error>>;

#[derive(Debug, Clone)]
struct ErrorMessage(String);

impl From<String> for ErrorMessage {
    fn from(other: String) -> Self {
        ErrorMessage(other)
    }
}

impl ErrorMessage {
    fn message(&self) -> &String {
        &self.0
    }
}

impl Display for ErrorMessage {
    fn fmt(&self, fmt: &mut Formatter) -> fmt::Result {
        write!(fmt, "{}", self.message())
    }
}

impl Error for ErrorMessage {
    fn description(&self) -> &str {
        self.message()
    }
}

#[derive(Debug, Clone, Copy)]
enum Wire {
    Up(usize),
    Down(usize),
    Left(usize),
    Right(usize),
}

impl Wire {
    fn magnitude(&self) -> usize {
        match self {
            Wire::Up(m)
            | Wire::Down(m)
            | Wire::Left(m)
            | Wire::Right(m) => *m
        }
    }

    fn add_pos(&self, (x, y): (isize, isize)) -> (isize, isize) {
        let (x0, y0) = match self {
            Wire::Up(y0) => (0, -(*y0 as isize)),
            Wire::Down(y0) => (0, *y0 as isize),
            Wire::Left(x0) => (-(*x0 as isize), 0),
            Wire::Right(x0) => (*x0 as isize, 0),
        };
        (x + x0, y + y0)
    }
}

impl FromStr for Wire {
    type Err = ErrorMessage;

    fn from_str(s: &str) -> std::result::Result<Self, Self::Err> {
        let num = s[1..].parse::<usize>()
            .map_err(|e| ErrorMessage(e.description().to_string()))?;
        let c = s.chars().nth(0)
            .ok_or_else(|| ErrorMessage("expected U, D, L, or R followed by a number".to_string()))?;
        match c {
            'U' => Ok(Wire::Up(num)),
            'D' => Ok(Wire::Down(num)),
            'L' => Ok(Wire::Left(num)),
            'R' => Ok(Wire::Right(num)),
            _ => Err(ErrorMessage("expected U, D, L, or R followed by a number".to_string())),
        }
    }
}

#[derive(Debug, Clone, Copy, Default)]
struct Cell {
    pass: usize,
    steps: [usize; 2],
}

const FIRST_PASS: usize = 1;
const SECOND_PASS: usize = 2;
const BOTH_PASS: usize = FIRST_PASS | SECOND_PASS;

#[derive(Debug)]
struct Board {
    board: Vec<Vec<Cell>>,
    pos: (isize, isize),
    origin: (isize, isize),
    steps: usize,
}

impl Default for Board {
    fn default() -> Self {
        Board {
            board: vec![vec![Default::default()]],
            pos: Default::default(),
            origin: Default::default(),
            steps: Default::default(),
        }
    }
}

impl Display for Board {
    fn fmt(&self, fmt: &mut Formatter) -> fmt::Result {
        for (y, row) in self.board.iter().enumerate() {
            let y = y as isize;
            for (x, col) in row.iter().enumerate() {
                let x = x as isize;
                let c = if (x, y) == self.origin {
                    'o'
                } else if (x, y) == self.pos {
                    '*'
                } else if col.pass > 0 {
                    '+'
                } else {
                    '.'
                };
                write!(fmt, "{}", c)?;
            }
            writeln!(fmt)?;
        }
        Ok(())
    }
}

impl Board {
    fn x(&self) -> isize { 
        self.pos.0
    }

    fn y(&self) -> isize {
        self.pos.1
    }

    fn origin_x(&self) -> isize {
        self.origin.0
    }

    fn origin_y(&self) -> isize {
        self.origin.1
    }

    fn min_x(&self) -> isize {
        -self.origin_x()
    }

    fn min_y(&self) -> isize {
        -self.origin_y()
    }

    fn max_x(&self) -> isize {
        self.board_w() - self.origin_x()
    }

    fn max_y(&self) -> isize {
        self.board_h() - self.origin_y()
    }

    fn board_w(&self) -> isize {
        if self.board.is_empty() {
            0
        } else {
            self.board[0].len() as isize
        }
    }

    fn board_h(&self) -> isize {
        self.board.len() as isize
    }

    fn ensure_pos(&mut self, (pos_x, pos_y): (isize, isize)) {
        self.ensure_y_pos(pos_y);
        self.ensure_x_pos(pos_x);
    }

    fn ensure_x_pos(&mut self, pos_x: isize) {
        if pos_x >= self.max_x() {
            let amount = pos_x - self.max_x() + 1;
            self.grow_right(amount as usize);
        } else if pos_x <= self.min_x() {
            let amount = (self.min_x() - pos_x).abs() + 1;
            self.grow_left(amount as usize);
        }
    }

    fn ensure_y_pos(&mut self, pos_y: isize) {
        if pos_y >= self.max_y() {
            let amount = pos_y - self.max_y() + 1;
            self.grow_down(amount as usize);
        } else if pos_y <= self.min_y() {
            let amount = (self.min_y() - pos_y).abs() + 1;
            self.grow_up(amount as usize);
        }
    }

    fn grow_down(&mut self, amount: usize) {
        let rows = vec!(vec!(Default::default(); self.board_w() as usize); amount);
        self.board.extend(rows);
    }

    fn grow_up(&mut self, amount: usize) {
        let w = self.board_w();
        let rows = mem::replace(&mut self.board, vec!(vec!(Default::default(); w as usize); amount));
        self.board.extend(rows);
        self.origin.1 += amount as isize;
    }

    fn grow_left(&mut self, amount: usize) {
        for row in self.board.iter_mut() {
            let row_remainder = mem::replace(row, vec!(Default::default(); amount));
            row.extend(row_remainder);
        }
        self.origin.0 += amount as isize;
    }

    fn grow_right(&mut self, amount: usize) {
        for row in self.board.iter_mut() {
            row.extend(vec!(Cell::default(); amount));
        }
    }

    fn apply_wire(&mut self, wire: Wire, which_pass: usize) -> Vec<(Cell, isize, isize)> {
        let end_pos = wire.add_pos(self.pos);
        self.ensure_pos(end_pos);
        let x = (self.x() + self.origin_x()) as usize;
        let y = (self.y() + self.origin_y()) as usize;

        /*
        println!("applying wire {:?}", wire);
        println!("pos: {:?}", self.pos);
        println!("end pos: {:?}", end_pos);
        println!("origin: {:?}", self.origin);
        println!("start pos: {:?}", (x, y));
        println!("size: {:?}", self.board_size());
        */

        let mut crossings = Vec::new();
        let step_index = which_pass - 1;
        match wire {
            Wire::Up(amount) => for offset in 0..amount {
                let y0 = y - offset;
                self.board[y0][x].pass |= which_pass;

                if self.board[y0][x].steps[step_index] == 0 {
                    self.board[y0][x].steps[step_index] = self.steps + offset;
                }

                if self.board[y0][x].pass == BOTH_PASS {
                    let cell = self.board[y0][x];
                    crossings.push((cell, self.x(), self.y() - (offset as isize)));
                }
            }
            Wire::Down(amount) => for offset in 0..amount {
                let y0 = y + offset;
                self.board[y0][x].pass |= which_pass;

                if self.board[y0][x].steps[step_index] == 0 {
                    self.board[y0][x].steps[step_index] = self.steps + offset;
                }

                if self.board[y0][x].pass == BOTH_PASS {
                    let cell = self.board[y0][x];
                    crossings.push((cell, self.x(), self.y() + (offset as isize)));
                }
            }
            Wire::Left(amount) => for offset in 0..amount {
                let x0 = x - offset;
                self.board[y][x0].pass |= which_pass;

                if self.board[y][x0].steps[step_index] == 0 {
                    self.board[y][x0].steps[step_index] = self.steps + offset;
                }

                if self.board[y][x0].pass == BOTH_PASS {
                    let cell = self.board[y][x0];
                    crossings.push((cell, self.x() - (offset as isize), self.y()));
                }
            }
            Wire::Right(amount) => for offset in 0..amount {
                let x0 = x + offset;
                self.board[y][x0].pass |= which_pass;

                if self.board[y][x0].steps[step_index] == 0 {
                    self.board[y][x0].steps[step_index] = self.steps + offset;
                }

                if self.board[y][x0].pass == BOTH_PASS {
                    let cell = self.board[y][x0];
                    crossings.push((cell, self.x() + (offset as isize), self.y()));
                }
            }
        }
        self.steps += wire.magnitude();
        self.pos = end_pos;
        crossings.retain(|(_, x, y)| (*x, *y) != (0, 0));
        crossings
    }

    fn reset_pos(&mut self) {
        self.steps = 0;
        self.pos = (0, 0);
    }
}

fn get_input_string() -> io::Result<String> {
    let mut buffer = String::new();
    io::stdin().read_to_string(&mut buffer)?;
    Ok(buffer)
}

fn main() -> Result<()> {
    let input = get_input_string()?;
    let mut lines = input
        .trim()
        .lines()
        .map(|line| line.trim()
             .split(",")
             .map(|wire| wire.parse::<Wire>().map_err(From::from))
             .collect::<Result<Vec<_>>>());
    let wires1 = lines.next()
        .expect("two lines of input")?;
    let wires2 = lines.next()
        .expect("two lines of input")?;

    day3(&wires1, &wires2);
    Ok(())
}

fn day3(wires1: &Vec<Wire>, wires2: &Vec<Wire>) {
    let mut board = Board::default();

    for wire in wires1.iter() {
        board.apply_wire(*wire, FIRST_PASS);
    }
    board.reset_pos();

    let mut crossings = Vec::new();
    for wire in wires2.iter() {
        crossings.extend(board.apply_wire(*wire, SECOND_PASS));
    }
    //println!("{}", board);
    //println!("{:#?}", crossings);
    let shortest: isize = crossings.iter()
        .map(|(_, x, y)| x.abs() + y.abs())
        .min()
        .unwrap();
    println!("Part 1: {}", shortest);

    let fewest: usize = crossings.iter()
        .map(|(cell, _, _)| cell.steps[0] + cell.steps[1])
        .min()
        .unwrap();
    println!("Part 2: {}", fewest);
}