Advent-of-Code-2022/17/solution.mjs

import { readFileSync } from 'node:fs';

const input = readFileSync('input', 'utf-8');


const shapePatterns = `
  ####   #     #  #  ##
        ###    #  #  ##
         #   ###  #
                  #
`;

function isTouching(coordA, coordB) {
  return (
    (coordA[0] === coordB[0] && Math.abs(coordA[1] - coordB[1]) === 1) ||
    (coordA[1] === coordB[1] && Math.abs(coordA[0] - coordB[0]) === 1)
  );
}

function isEqual(coordA, coordB) {
  return coordA[0] === coordB[0] && coordA[1] === coordB[1];
}

function getAllConnected(coords, coordA) {
  const connected = coords.filter(coordB => isTouching(coordA, coordB));
  if (!connected.length) {
    return [coordA];
  }
  const notConnected = coords.filter(coordC =>
    !isEqual(coordC, coordA) &&
    !connected.find(coordD => isEqual(coordC, coordD))
  );
  return [
    coordA,
    ...connected
      .flatMap(coordE => getAllConnected(notConnected, coordE))
      .filter((coordF, i, connectedCoords) => connectedCoords.findLastIndex(
        coordG => isEqual(coordF, coordG)
      ) === i)
  ];
}

class Shape {
  constructor(coords, id) {
    this.id = id;

    if (!coords.length) {
      throw new Error('Empty shape coords');
    }

    // Normalize coords
    const minX = coords.reduce((min, [x, _]) => Math.min(min, x), Infinity);
    const minY = coords.reduce((min, [_, y]) => Math.min(min, y), Infinity);
 
    coords = coords.map(([x, y]) => [x - minX, y - minY]);
    this.coords = coords;

    this.width = 1 + coords.reduce((max, [x, _]) => Math.max(max, x), 0);
    this.height = 1 + coords.reduce((max, [_, y]) => Math.max(max, y), 0);
  }
}

function getShapes(patterns) {
  let shapeCoords = patterns
    .split('\n')
    .flatMap((line, y) => line
      .split('')
      .flatMap((c, x) => c === '#' ? [[x, y]] : [])
    );

  const shapes = [];
  while (shapeCoords.length) {
    const shape = getAllConnected(shapeCoords, shapeCoords[0]);
    shapeCoords = shapeCoords.filter(coordA => !shape.find(coordB =>
      isEqual(coordA, coordB)
    ));
    shapes.push(shape);
  }

  return shapes.map((coords, i) => new Shape(coords, i));
}


class Chamber {
  constructor(width) {
    this.width = width;
    this.rows = [];
    this.placements = [];
  }

  get height() {
    return this.rows.length;
  }

  get rockCount() {
    return this.placements.length;
  }

  // Test if a shape will collide with anything at the given coordinates
  collides(shape, x, y) {
    for (const coord of shape.coords) {
      const gX = x + coord[0];
      const gY = y - coord[1];

      if (gX < 0 || gX > this.width - 1 || gY < 0) {
        return true;
      }

      if (gY > this.rows.length - 1) {
        continue;
      }

      if (this.rows[gY][gX] !== ' ') {
        return true;
      }
    }
    return false;
  }

  // Add a shape at the given coordinates
  add(shape, x, y) {
    const nRowsAdded = Math.max(0, y + 1 - this.rows.length);
    if (nRowsAdded > 0) {
      this.rows.push(...new Array(nRowsAdded).fill(' '.repeat(this.width)));
    }

    const lastY = this.placements.length ?
      this.placements[this.placements.length - 1].y :
      0;

    this.placements.push({
      shapeId: shape.id,
      x,
      y,
      relativeY: y - lastY
    });

    for (const coord of shape.coords) {
      const gX = x + coord[0];
      const gY = y - coord[1];
      this.rows[gY] = (
        this.rows[gY].slice(0, gX) +
        '#' +
        this.rows[gY].slice(gX + 1)
      );
    }
  }

  print() {
    for (let i = this.rows.length - 1; i >= 0; i--) {
      console.log(this.rows[i]);
    }
  }
}

const shapes = getShapes(shapePatterns);

function* jetGenerator() {
  while (true) {
    for (const jet of input.split('').filter(c => /[<>]/.test(c))) {
      yield jet === '<' ? -1 : 1;
    }
  }
}

function* rockGenerator() {
  while (true) {
    for (const shape of shapes) {
      yield shape;
    }
  }
}


const chamber = new Chamber(7);

const jets = jetGenerator();
const rocks = rockGenerator();


function processRock() {
  const rock = rocks.next().value;

  let x = 2;
  let y = chamber.height + 2 + rock.height;

  while (true) {
    const jet = jets.next().value;
    if (!chamber.collides(rock, x + jet, y)) {
      x += jet;
    }

    if (!chamber.collides(rock, x, y - 1)) {
      y -= 1;
    } else {
      chamber.add(rock, x, y);
      break;
    }
  }
}


while (chamber.rockCount < 2022) {
  processRock();
}

console.log(
  `The tower will be: ${chamber.height} units tall after 2022 rocks`
);


function findRepetition(source, isEqual) {
  let halfSize = Math.floor(source.length / 2);

  while (halfSize > 0) {
    let skip = false;
    for (let i = 0; i < halfSize; i++) {
      const first = source[source.length - (2 * halfSize) + i];
      const second = source[source.length - halfSize + i];
      if (!isEqual(first, second)) {
        skip = true;
        break;
      }
    }
    if (!skip) {
      return halfSize;
    }
    halfSize--;
  }
}

// Add rocks until a period of repetition can be identified
function findPeriodOfRepetition() {
  while (true) {
    const periodOfRepetition = findRepetition(chamber.placements, (p1, p2) =>
      p1.shapeId === p2.shapeId &&
      p1.x === p2.x &&
      p1.relativeY === p2.relativeY
    );
    if (periodOfRepetition !== undefined) {
      return periodOfRepetition;
    }
    // Add 1000 rocks
    for (let i = 0; i < 1000; i++) {
      processRock();
    }
  }
}

const periodOfRepetition = findPeriodOfRepetition();
let changeInHeight;

// Confirm period of repetition
for (let round = 0; round < 5; round++) {
  const initialHeight = chamber.height;

  // Add period of repetition rocks
  for (let i = 0; i < periodOfRepetition; i++) {
    processRock();
  }

  const change = chamber.height - initialHeight;
  if (changeInHeight === undefined) {
    changeInHeight = change;
  } else {
    if (changeInHeight !== change) {
      throw new Error(
        `Unable to confirm period of repetition, expected change in height ` +
          `of: ${changeInHeight}, got ${change}`
      );
    }
  }
}

const rockTarget = 1000000000000;

const rocksRemaining = rockTarget - chamber.rockCount;
const multiple = Math.floor(rocksRemaining / periodOfRepetition);
const remainder = rocksRemaining % periodOfRepetition;

// Add remaining rocks
for (let i = 0; i < remainder; i++) {
  processRock();
}

const targetRockHeight = chamber.height + multiple * changeInHeight;

console.log(
  `The tower will be: ${targetRockHeight} units tall after ${rockTarget} rocks`
);