advent-of-code/2020/17/solution2.js

const fs = require("fs");

const input = fs.readFileSync("input", "utf-8").trim();
const startPlane = input.split("\n").map((line) => line.split(""));

let pocket = [[startPlane]];

function main() {
  for (let step = 1; step <= 6; step++) {
    const countActive = cycle();
    console.log(`After ${step} steps: ${countActive}`);
  }
}

function cycle() {
  let squareLength = pocket[0][0].length;
  let countActive = 0;
  const nextPocket = [];
  for (let w = -1; w < pocket.length + 1; w++) {
    const space = [];
    for (let z = -1; z < pocket.length + 1; z++) {
      const plane = [];
      for (let x = -1; x < squareLength + 1; x++) {
        const line = [];
        for (let y = -1; y < squareLength + 1; y++) {
          const nextState = getState(w, z, x, y);
          if (nextState === "#") countActive++;
          line.push(nextState);
        }
        plane.push(line);
      }
      space.push(plane);
    }
    nextPocket.push(space);
  }
  pocket = nextPocket;

  return countActive;
}

function getState(pw, pz, px, py) {
  let activeNeighbors = 0;
  for (const w of range(pw - 1, pw + 2)) {
    for (const z of range(pz - 1, pz + 2)) {
      for (const x of range(px - 1, px + 2)) {
        for (const y of range(py - 1, py + 2)) {
          if (pw === w && pz === z && px === x && py === y) continue;
          if (isActive(w, z, x, y)) activeNeighbors++;
        }
      }
    }
  }
  // console.log(`${py},${px},${py}: ${activeNeighbors}`);
  if (isActive(pw, pz, px, py)) {
    return activeNeighbors === 2 || activeNeighbors === 3 ? "#" : ".";
  } else {
    return activeNeighbors === 3 ? "#" : ".";
  }
}

function isActive(w, z, x, y) {
  return pocket[w]?.[z]?.[x]?.[y] === "#";
}

function range(start, stop, increment = 1) {
  if (typeof stop === "undefined") {
    stop = start;
    start = 0;
  }
  const r = [];
  for (let i = start; i < stop; i += increment) {
    r.push(i);
  }
  return r;
}

main();