jsadvent/solutions/2016/1.js

const { Glib, Vector } = require('../../lib');

const DIRECTIONS = {
  NORTH: 'NORTH',
  SOUTH: 'SOUTH',
  EAST: 'EAST',
  WEST: 'WEST',
};

const TURNS = {
  LEFT: 'L',
  RIGHT: 'R',
};

const TURN = {
  [TURNS.LEFT]: {
    [DIRECTIONS.NORTH]: DIRECTIONS.WEST,
    [DIRECTIONS.EAST]: DIRECTIONS.NORTH,
    [DIRECTIONS.SOUTH]: DIRECTIONS.EAST,
    [DIRECTIONS.WEST]: DIRECTIONS.SOUTH,
  },
  [TURNS.RIGHT]: {
    [DIRECTIONS.NORTH]: DIRECTIONS.EAST,
    [DIRECTIONS.EAST]: DIRECTIONS.SOUTH,
    [DIRECTIONS.SOUTH]: DIRECTIONS.WEST,
    [DIRECTIONS.WEST]: DIRECTIONS.NORTH,
  },
};

const MOVE = {
  [DIRECTIONS.NORTH]: new Vector(0, 1),
  [DIRECTIONS.EAST]: new Vector(1, 0),
  [DIRECTIONS.SOUTH]: new Vector(0, -1),
  [DIRECTIONS.WEST]: new Vector(-1, 0),
};

const START = new Vector(0, 0);

const parse = (input) =>
  Glib.fromIterable(input.trim().split(',')).map((i) => {
    const [turn, ...distance] = i.trim();

    if (turn !== TURNS.LEFT && turn !== TURNS.RIGHT) {
      throw new Error('Invalid turn');
    }

    return {
      turn,
      distance: parseInt(distance.join(''), 10),
    };
  });

module.exports = {
  '1': (input) => {
    input = parse(input);
    let direction = DIRECTIONS.NORTH;
    let location = START;
    for (const { turn, distance } of input) {
      direction = TURN[turn][direction];
      const moveVector = MOVE[direction].multiply(distance);
      location = location.add(moveVector);
    }
    return START.distance(location);
  },
  '2': (input) => {
    input = parse(input);
    let direction = DIRECTIONS.NORTH;
    let location = START;

    let visited = new Set();
    for (const { turn, distance } of input) {
      direction = TURN[turn][direction];
      const destination = location.add(MOVE[direction].multiply(distance))
        .string;
      let locStr = location.string;
      while (locStr != destination) {
        if (visited.has(locStr)) {
          return START.distance(location);
        }
        visited.add(locStr);
        location = location.add(MOVE[direction]);
        locStr = location.string;
      }
    }
  },
  parse,
};