jsadvent/solutions/2017/3.js

const {
  Glib,
  BNMath: Math,
  Vector,
  twodee: { DIRECTIONS, ORIGIN },
} = require('../../lib');

const midpointDistance = (i) => (Math.sqrt(i - 1n) + 1n) / 2n;
const rotationalDistance = (i, md) => {
  if (i === 1n) {
    return 0n;
  }
  const sideLength = md * 2n;
  const rotationalOffset = i - ((md * 2n - 1n) ** 2n + 1n);
  const normalizedRotationalOffset = rotationalOffset % sideLength;
  const sideOffset = -md + 1n;
  return Math.abs(normalizedRotationalOffset + sideOffset);
};

const distance = (i) => {
  const md = midpointDistance(i);
  const rd = rotationalDistance(i, md);
  // console.log(i, md, rd);
  return md + rd;
};

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

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

const nextDirection = (current, direction, calculated) =>
  calculated.has(current.add(check.get(direction.string)).string)
    ? direction
    : order.get(direction.string);

const validate = [
  1n,
  1n,
  2n,
  4n,
  5n,
  10n,
  11n,
  23n,
  25n,
  26n,
  54n,
  57n,
  59n,
  122n,
  133n,
  142n,
  147n,
  304n,
  330n,
  351n,
  362n,
  747n,
  806n,
  880n,
  931n,
  957n,
  1968n,
  2105n,
  2275n,
  2391n,
  2450n,
  5022n,
  5336n,
  5733n,
  6155n,
  6444n,
  6591n,
  13486n,
  14267n,
  15252n,
  16295n,
  17008n,
  17370n,
  35487n,
  37402n,
  39835n,
  42452n,
  45220n,
  47108n,
  48065n,
  98098n,
  103128n,
  109476n,
  116247n,
  123363n,
  128204n,
  130654n,
  266330n,
  279138n,
  295229n,
  312453n,
  330785n,
  349975n,
  363010n,
  369601n,
  752688n,
  787032n,
  830037n,
  875851n,
  924406n,
  975079n,
  1009457n,
  1026827n,
  2089141n,
  2179400n,
  2292124n,
  2411813n,
  2539320n,
  2674100n,
  2814493n,
  2909666n,
  2957731n,
  6013560n,
  6262851n,
];

module.exports = {
  '1': (input) => {
    return distance(BigInt(input));
  },
  '2': (input) => {
    const target = BigInt(input);
    const calculated = new Map([[ORIGIN.string, 1n]]);
    let direction = DIRECTIONS.UP;
    let current = DIRECTIONS.RIGHT;
    let sum = 1n;
    while (sum < target) {
      sum = current
        .neighbors()
        .map((pt) => pt.string)
        .lookupInMap(calculated, true)
        .sum();
      calculated.set(current.string, sum);
      current = current.add(direction);
      direction = nextDirection(current, direction, calculated);
    }
    return sum;

    a.filter(
      (char, index) =>
        char === input[(index + input.length / 2) % input.length],
    )
      .toInts()
      .sum();
  },
};