jsadvent/solutions/2020/12.js

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

const LEFT = new Map([
  [twodee.DIRECTIONS.UP.string, twodee.DIRECTIONS.LEFT],
  [twodee.DIRECTIONS.LEFT.string, twodee.DIRECTIONS.DOWN],
  [twodee.DIRECTIONS.DOWN.string, twodee.DIRECTIONS.RIGHT],
  [twodee.DIRECTIONS.RIGHT.string, twodee.DIRECTIONS.UP],
]);

const RIGHT = new Map([
  [twodee.DIRECTIONS.UP.string, twodee.DIRECTIONS.RIGHT],
  [twodee.DIRECTIONS.RIGHT.string, twodee.DIRECTIONS.DOWN],
  [twodee.DIRECTIONS.DOWN.string, twodee.DIRECTIONS.LEFT],
  [twodee.DIRECTIONS.LEFT.string, twodee.DIRECTIONS.UP],
]);

const INSTRUCTIONS1 = {
  N: (count, state) => {
    return {
      ...state,
      location: state.location.add(twodee.DIRECTIONS.UP.multiply(count)),
    };
  },
  S: (count, state) => {
    return {
      ...state,
      location: state.location.add(twodee.DIRECTIONS.DOWN.multiply(count)),
    };
  },
  E: (count, state) => {
    return {
      ...state,
      location: state.location.add(twodee.DIRECTIONS.RIGHT.multiply(count)),
    };
  },
  W: (count, state) => {
    return {
      ...state,
      location: state.location.add(twodee.DIRECTIONS.LEFT.multiply(count)),
    };
  },
  F: (count, state) => {
    return {
      ...state,
      location: state.location.add(state.direction.multiply(count)),
    };
  },
  L: (count, state) => {
    let direction = state.direction;
    for (let i = 0; i < count; i += 90) {
      direction = LEFT.get(direction.string);
    }
    return {
      ...state,
      direction,
    };
  },
  R: (count, state) => {
    let direction = state.direction;
    for (let i = 0; i < count; i += 90) {
      direction = RIGHT.get(direction.string);
    }
    return {
      ...state,
      direction,
    };
  },
};

const INSTRUCTIONS2 = {
  ...INSTRUCTIONS1,
  F: (count, state) => {
    return {
      ...state,
      ship: state.ship.add(state.location.multiply(count)),
    };
  },
  // todo: (soon) implement a matrix library so this gets better
  L: (count, state) => {
    let location = state.location;
    for (let i = 0; i < count; i += 90) {
      location = new Vector(-location.v[1], location.v[0]);
    }
    return {
      ...state,
      location,
    };
  },
  R: (count, state) => {
    let location = state.location;
    for (let i = 0; i < count; i += 90) {
      location = new Vector(location.v[1], -location.v[0]);
    }
    return {
      ...state,
      location,
    };
  },
};

const solve = (input, ops, start = twodee.ORIGIN) =>
  Glib.fromLines(input, ops)
    .map(([instruction, ...number]) => ({
      instruction,
      count: BigInt(number.join('')),
    }))
    .reduce(
      (state, { instruction, count }) => {
        return ops[instruction](count, state);
      },
      {
        location: start,
        direction: twodee.DIRECTIONS.RIGHT,
        ship: twodee.ORIGIN,
      },
    );

module.exports = {
  1: (input) => solve(input, INSTRUCTIONS1).location.distance(twodee.ORIGIN),
  2: (input) =>
    solve(input, INSTRUCTIONS2, new Vector(10, 1)).ship.distance(twodee.ORIGIN),
};