advent-of-code/2020/20/solution2.js

/**
 * TODO: optimize for reduced complexity
 * TODO: optimize for cleaner code
 */

const fs = require("fs");

function main() {
  const input = fs.readFileSync("input", "utf-8").trim();
  const tiles = input.split("\n\n").map((tile) => new Tile(tile));
  const tilesMap = Object.fromEntries(tiles.map((tile) => [tile.id, tile]));
  const tileSet = new Set(tiles);
  // console.log(tiles);
  // console.log(tileSet);

  const borderMap = {};
  for (const tile of tiles) {
    for (const border of Object.values(tile.borders)) {
      const key = canonical(border);
      if (typeof borderMap[key] === "undefined") {
        borderMap[key] = [];
      }
      borderMap[key].push(tile.id);
      if (borderMap[key].length > 2) {
        console.warn(
          "Assumption does not hold: One edge is present in more than two tiles"
        );
      }
    }
  }
  // console.log(borderMap);

  const edgeTiles = new Set();
  const cornerTiles = new Set();
  const neighbors = {};

  for (const ids of Object.values(borderMap)) {
    if (ids.length === 1) {
      const id = ids[0];
      if (edgeTiles.has(id)) {
        edgeTiles.delete(id);
        cornerTiles.add(id);
      } else {
        edgeTiles.add(id);
      }
    } else {
      const [tileA, tileB] = ids;
      if (typeof neighbors[tileA] === "undefined") neighbors[tileA] = [];
      if (typeof neighbors[tileB] === "undefined") neighbors[tileB] = [];
      neighbors[tileA].push(tileB);
      neighbors[tileB].push(tileA);
    }
  }
  console.log(neighbors);
  let topLeft = tilesMap[Array.from(cornerTiles)[0]];
  console.log("TopLeft:", topLeft.id);

  const isEdge = (border) => borderMap[canonical(border)].length === 1;

  console.log(topLeft.pprint());
  const reprs = [];
  for (const t of allOrientations(topLeft)) {
    reprs.push(t.pprint().split("\n"));
  }
  for (let i = 0; i < reprs[0].length; i++) {
    for (let j = 0; j < reprs.length; j++) {
      process.stdout.write(reprs[j][i]);
      process.stdout.write("  ");
    }
    process.stdout.write("\n");
  }

  while (isEdge(topLeft.borders.e) || isEdge(topLeft.borders.s)) {
    console.log("rotating corner tile");
    topLeft.rot90();
  }
  // console.log(topLeft)
  tileSet.delete(topLeft);

  let curRow = [topLeft];
  const orderedTiles = [];
  const tileBuffer = Array.from(tileSet);

  let lastTile = topLeft;
  let loopDetection = 0;
  while (tileBuffer.length > 0) {
    // console.log("Tiles in buffer:", tileBuffer.length);
    let cur = tileBuffer.shift();

    if (isEdge(lastTile.borders.e)) {
      // console.log("Looking for southener of", topLeft.id, cur.id);
      for (cur of allOrientations(cur)) {
        if (reverse(topLeft.borders.s) === cur.borders.n) {
          orderedTiles.push(curRow);
          curRow = [];
          lastTile = cur;
          topLeft = cur;
          curRow.push(cur);
          break;
        }
      }
    } else {
      // console.log("Looking for eastern of", lastTile.id, cur.id);
      for (cur of allOrientations(cur)) {
        if (lastTile.borders.e === reverse(cur.borders.w)) {
          lastTile = cur;
          curRow.push(cur);
          break;
        }
      }
    }
    if (cur !== lastTile) {
      tileBuffer.push(cur);
    } else {
      // console.log("Tile found! Its", cur.id);
      loopDetection = 0;
    }
    // sleep(50);
    if (loopDetection > tileBuffer.length) {
      console.log("loop detected");
      break;
    }
    loopDetection++;
  }
  orderedTiles.push(curRow);
  console.log("Found map arrangement");
  console.log(orderedTiles);

  let map = "";
  for (const row of orderedTiles) {
    for (let i = 0; i < row[0].content.length; i++) {
      for (let j = 0; j < row.length; j++) {
        map += row[j].content[i].join("");
        // map += " ";
      }
      map += "\n";
    }
    // map += "\n";
  }
  const hashCount = map.match(/#/g).length;
  console.log("hashCount", hashCount);
  // console.log(map);
  map = map.split("\n").map((row) => row.split(""));

  let sumSeamonsters;
  for (let i = 0; i < 8; i++) {
    if (i === 4) {
      console.log("flip map");
      map = flipH(map);
    } else {
      console.log("rotate map");
      map = rotSquare(map);
    }

    sumSeamonsters = findSeamonster(map);
    console.log("Seamonsters found:", sumSeamonsters);
    if (sumSeamonsters) {
      break;
    }
  }
  const seamonsterHashes = 15 * sumSeamonsters;
  console.log(hashCount - seamonsterHashes);
}

const reverse = (str) => str.split("").reverse().join("");
const isCanonical = (edge) => edge < reverse(edge);
const canonical = (edge) => (isCanonical(edge) ? edge : reverse(edge));
const trimEnds = (arr) => arr.slice(1, arr.length - 1);
function rotSquare(mat) {
  const result = [];
  const length = mat.length;
  for (let i = 0; i < length; i++) {
    const row = [];
    for (let j = 0; j < length; j++) {
      row.push(mat[length - 1 - j][i]);
    }
    result.push(row);
  }
  return result;
}
const flipH = (mat) => mat.map((row) => row.reverse());
const flipV = (mat) => mat.reverse();
function* allOrientations(tile) {
  tile.rot90();
  yield tile;
  tile.rot90();
  yield tile;
  tile.rot90();
  yield tile;
  tile.rot90();
  yield tile;
  tile.flipH();
  yield tile;
  tile.rot90();
  yield tile;
  tile.rot90();
  yield tile;
  tile.rot90();
  yield tile;
}

function findSeamonster(map) {
  map = map.map((row) => row.join(""));
  const sm1 = "                  # ";
  const sm2 = "#    ##    ##    ###";
  const sm3 = " #  #  #  #  #  #   ";
  const pattern1 = new RegExp(`(?=${sm1.replaceAll(" ", ".")})`, "g");
  const pattern2 = new RegExp(`(?=${sm2.replaceAll(" ", ".")})`, "g");
  const pattern3 = new RegExp(`(?=${sm3.replaceAll(" ", ".")})`, "g");

  let sum = 0;
  for (let lineIdx = 0; lineIdx < map.length - 3; lineIdx++) {
    const [line1, line2, line3] = map.slice(lineIdx, lineIdx + 3);
    let solutions1 = new Set();
    let solutions2 = new Set();
    let solutions3 = new Set();
    // console.log("Processing line", lineIdx, line1);
    for (const match of line1.matchAll(pattern1)) {
      solutions1.add(match.index);
    }
    // console.log(solutions1);
    for (const match of line2.matchAll(pattern2)) {
      if (solutions1.has(match.index)) solutions2.add(match.index);
    }
    // console.log(solutions2);
    for (const match of line3.matchAll(pattern3)) {
      if (solutions2.has(match.index)) solutions3.add(match.index);
    }
    // console.log(solutions3);
    if (solutions3.size) {
      for (const idx of solutions3) {
        console.log(`Seamonster found at [${lineIdx}, ${idx}]`);
      }
    }
    sum += solutions3.size;
  }
  return sum;
}

const rot90Map = { n: "w", w: "s", s: "e", e: "n" };
const flipHMap = { w: "e", e: "w" };
const flipVMap = { n: "s", s: "n" };

function applyMap(map, obj, doReverse = false) {
  const result = {};
  for (const [target, source] of Object.entries(map)) {
    if (obj[source] === undefined) {
      console.log(source, obj);
      throw Error("aa");
    }
    result[target] = doReverse ? reverse(obj[source]) : obj[source];
  }
  return { ...obj, ...result };
}

class Tile {
  constructor(rawInput) {
    const lines = rawInput.split("\n");
    this.id = lines.shift().match("[0-9]+")[0];
    this.borders = {
      n: lines[0],
      e: lines.map((line) => line[line.length - 1]).join(""),
      s: reverse(lines[lines.length - 1]),
      w: reverse(lines.map((line) => line[0]).join("")),
    };
    this.content = trimEnds(lines)
      .map(trimEnds)
      .map((line) => line.split(""));
  }

  rot90(times = 1) {
    while (times--) {
      this.borders = applyMap(rot90Map, this.borders);
      this.content = rotSquare(this.content);
    }
  }

  flipH() {
    this.borders = applyMap(flipHMap, this.borders, true);
    this.borders.n = reverse(this.borders.n);
    this.borders.s = reverse(this.borders.s);
    this.content.map((row) => row.reverse());
  }

  flipV() {
    this.borders = applyMap(flipVMap, this.borders, true);
    this.borders.w = reverse(this.borders.w);
    this.borders.e = reverse(this.borders.e);
    this.content.reverse();
  }

  pprint() {
    let str = "";
    str += " " + this.borders.n + " \n";
    for (let i = 0; i < this.borders.w.length; i++) {
      str += reverse(this.borders.w)[i];
      if (i === 0 || i === this.borders.w.length - 1) {
        str += " ".repeat(this.borders.w.length);
      } else {
        str += " " + this.content[i - 1].join("") + " ";
      }
      str += this.borders.e[i];
      str += "\n";
    }
    str += " " + reverse(this.borders.s) + " ";
    return str;
  }
}

main();