Advent-of-Code-2022/23/solution.mjs

import { readFileSync } from 'node:fs';

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

export class InfiniteGrid {
  constructor() {
    this.ox = null;
    this.oy = null;
    this.rows = [];
  }

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

  get width() {
    return this.rows[0]?.length ?? 0;
  }

  get(x, y) {
    return this.rows[y - (this.oy ?? y)]?.[x - (this.ox ?? x)];
  }

  set(x, y, v) {
    this.expandToFit(x, y);
    
    const ax = x - this.ox;
    const ay = y - this.oy;

    this.rows[ay][ax] = v;
  }

  expandToFit(x, y) {
    if (this.ox === null) this.ox = x;
    if (this.oy === null) this.oy = y;

    const left = Math.max(0, this.ox - x);
    const up = Math.max(0, this.oy - y);
    const right = Math.max(0, (x - this.ox + 1) - this.width);
    const down = Math.max(0, (y - this.oy + 1) - this.height);
    
    if (up || right || down || left) {
      this.rows = [
        ...new Array(up).fill(new Array(this.width + left + right).fill()),
        ...this.rows.map(row =>
          [...new Array(left), ...row, ...new Array(right)]
        ),
        ...new Array(down).fill(new Array(this.width + left + right).fill())
      ];
    }

    this.ox -= left;
    this.oy -= up;
  }

  getBounds() {
    return {
      minX: this.ox,
      maxX: this.ox + (this.rows[0]?.length ?? 1) - 1,
      minY: this.oy,
      maxY: this.oy + (this.rows.length || 1) - 1
    };
  }

  printDefined() {
    console.log(this.rows
      .map(row => row
        .map(cell => cell ? '#' : '.')
        .join('')
      )
      .join('\n')
    );
  }

  countEmpty() {
    return this.rows.reduce(
      (total, row) => total + row.reduce(
        (rowTotal, cell) => rowTotal + Number(!cell),
        0
      ),
      0
    );
  }
}

class Elf {
  constructor(grid) {
    this.grid = grid;
    this.pos = undefined;
  }

  moveTo(x, y) {
    if (this.pos) {
      this.grid.set(...this.pos, undefined);
    }
    this.pos = [x, y];
    this.grid.set(...this.pos, this);
  }

  proposePosition(directions) {
    if (!this.pos) throw new Error('Elf is not on the grid');

    const [x, y] = this.pos;
    const N = this.grid.get(x, y - 1);
    const NE = this.grid.get(x + 1, y - 1);
    const E = this.grid.get(x + 1, y);
    const SE = this.grid.get(x + 1, y + 1);
    const S = this.grid.get(x, y + 1);
    const SW = this.grid.get(x - 1, y + 1);
    const W = this.grid.get(x - 1, y);
    const NW = this.grid.get(x - 1, y - 1);

    if (!(N || NE || E || SE || S || SW || W || NW)) {
      // Don't move
      return;
    }

    for (const direction of directions) {
      if (direction === 'N' && !(NW || N || NE)) {
        return [x, y - 1];
      } else if (direction === 'E' && !(NE || E || SE)) {
        return [x + 1, y];
      } else if (direction === 'S' && !(SW || S || SE)) {
        return [x, y + 1];
      } else if (direction === 'W' && !(NW || W || SW)) {
        return [x - 1, y];
      }
    }
  }
}

const elfPositions = input
  .split('\n')
  .map(line => line.trim())
  .filter(line => !!line)
  .flatMap((line, y) => line
    .split('')
    .map((c, x) => {
      if (c === '#') {
        return [x, y];
      }
    })
    .filter(coords => !!coords)
  );

const grid = new InfiniteGrid();
const elves = [];
for (const pos of elfPositions) {
  const elf = new Elf(grid);
  elves.push(elf);
  elf.moveTo(...pos);
}
const directions = ['N', 'S', 'W', 'E'];
let round = 0;

function processRound() {
  const propositions = elves.flatMap(elf => {
    const pos = elf.proposePosition(directions);
    if (!pos) return [];
    return [{elf, x: pos[0], y: pos[1]}];
  });

  propositions.sort((p1, p2) => (p1.x - p2.x) || (p1.y - p2.y));
  const validPropositions = propositions
    .reduce((groups, proposition) => {
      if (groups.length) {
        const lastGroup = groups[groups.length - 1];
        const {x: lastX, y: lastY} = lastGroup[0];
        if (proposition.x === lastX && proposition.y === lastY) {
          lastGroup.push(proposition);
          return groups;
        }
      }

      groups.push([proposition]);
      return groups;
    }, [])
    .filter(group => group.length === 1)
    .flat();

  const moved = validPropositions.length;

  for (const proposition of validPropositions) {
    proposition.elf.moveTo(proposition.x, proposition.y);
  }
  
  // Reorder directions
  directions.push(directions.shift());

  round++;
  return moved;
}

do {
  processRound();
} while (round <= 10)
console.log('The number of empty ground tiles is:', grid.countEmpty());

while (processRound() !== 0) {};
console.log('The number of rounds to completion is:', round);