Day 17
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17/solution.mjs
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290
17/solution.mjs
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import { readFileSync } from 'node:fs';
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const input = readFileSync('input', 'utf-8');
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const shapePatterns = `
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#### # # # ##
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### # # ##
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# ### #
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#
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`;
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function isTouching(coordA, coordB) {
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return (
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(coordA[0] === coordB[0] && Math.abs(coordA[1] - coordB[1]) === 1) ||
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(coordA[1] === coordB[1] && Math.abs(coordA[0] - coordB[0]) === 1)
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);
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}
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function isEqual(coordA, coordB) {
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return coordA[0] === coordB[0] && coordA[1] === coordB[1];
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}
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function getAllConnected(coords, coordA) {
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const connected = coords.filter(coordB => isTouching(coordA, coordB));
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if (!connected.length) {
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return [coordA];
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}
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const notConnected = coords.filter(coordC =>
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!isEqual(coordC, coordA) &&
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!connected.find(coordD => isEqual(coordC, coordD))
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);
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return [
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coordA,
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...connected
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.flatMap(coordE => getAllConnected(notConnected, coordE))
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.filter((coordF, i, connectedCoords) => connectedCoords.findLastIndex(
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coordG => isEqual(coordF, coordG)
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) === i)
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];
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}
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class Shape {
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constructor(coords, id) {
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this.id = id;
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if (!coords.length) {
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throw new Error('Empty shape coords');
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}
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// Normalize coords
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const minX = coords.reduce((min, [x, _]) => Math.min(min, x), Infinity);
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const minY = coords.reduce((min, [_, y]) => Math.min(min, y), Infinity);
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coords = coords.map(([x, y]) => [x - minX, y - minY]);
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this.coords = coords;
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this.width = 1 + coords.reduce((max, [x, _]) => Math.max(max, x), 0);
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this.height = 1 + coords.reduce((max, [_, y]) => Math.max(max, y), 0);
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}
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}
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function getShapes(patterns) {
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let shapeCoords = patterns
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.split('\n')
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.flatMap((line, y) => line
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.split('')
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.flatMap((c, x) => c === '#' ? [[x, y]] : [])
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);
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const shapes = [];
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while (shapeCoords.length) {
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const shape = getAllConnected(shapeCoords, shapeCoords[0]);
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shapeCoords = shapeCoords.filter(coordA => !shape.find(coordB =>
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isEqual(coordA, coordB)
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));
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shapes.push(shape);
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}
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return shapes.map((coords, i) => new Shape(coords, i));
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}
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class Chamber {
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constructor(width) {
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this.width = width;
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this.rows = [];
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this.placements = [];
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}
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get height() {
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return this.rows.length;
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}
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get rockCount() {
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return this.placements.length;
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}
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// Test if a shape will collide with anything at the given coordinates
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collides(shape, x, y) {
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for (const coord of shape.coords) {
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const gX = x + coord[0];
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const gY = y - coord[1];
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if (gX < 0 || gX > this.width - 1 || gY < 0) {
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return true;
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}
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if (gY > this.rows.length - 1) {
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continue;
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}
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if (this.rows[gY][gX] !== ' ') {
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return true;
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}
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}
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return false;
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}
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// Add a shape at the given coordinates
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add(shape, x, y) {
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const nRowsAdded = Math.max(0, y + 1 - this.rows.length);
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if (nRowsAdded > 0) {
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this.rows.push(...new Array(nRowsAdded).fill(' '.repeat(this.width)));
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}
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const lastY = this.placements.length ?
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this.placements[this.placements.length - 1].y :
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0;
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this.placements.push({
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shapeId: shape.id,
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x,
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y,
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relativeY: y - lastY
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});
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for (const coord of shape.coords) {
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const gX = x + coord[0];
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const gY = y - coord[1];
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this.rows[gY] = (
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this.rows[gY].slice(0, gX) +
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'#' +
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this.rows[gY].slice(gX + 1)
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);
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}
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}
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print() {
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for (let i = this.rows.length - 1; i >= 0; i--) {
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console.log(this.rows[i]);
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}
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}
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}
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const shapes = getShapes(shapePatterns);
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function* jetGenerator() {
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while (true) {
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for (const jet of input.split('').filter(c => /[<>]/.test(c))) {
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yield jet === '<' ? -1 : 1;
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}
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}
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}
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function* rockGenerator() {
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while (true) {
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for (const shape of shapes) {
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yield shape;
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}
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}
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}
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const chamber = new Chamber(7);
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const jets = jetGenerator();
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const rocks = rockGenerator();
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function processRock() {
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const rock = rocks.next().value;
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let x = 2;
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let y = chamber.height + 2 + rock.height;
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while (true) {
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const jet = jets.next().value;
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if (!chamber.collides(rock, x + jet, y)) {
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x += jet;
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}
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if (!chamber.collides(rock, x, y - 1)) {
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y -= 1;
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} else {
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chamber.add(rock, x, y);
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break;
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}
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}
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}
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while (chamber.rockCount < 2022) {
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processRock();
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}
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console.log(
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`The tower will be: ${chamber.height} units tall after 2022 rocks`
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);
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function findRepetition(source, isEqual) {
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let halfSize = Math.floor(source.length / 2);
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while (halfSize > 0) {
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let skip = false;
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for (let i = 0; i < halfSize; i++) {
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const first = source[source.length - (2 * halfSize) + i];
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const second = source[source.length - halfSize + i];
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if (!isEqual(first, second)) {
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skip = true;
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break;
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}
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}
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if (!skip) {
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return halfSize;
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}
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halfSize--;
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}
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}
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// Add rocks until a period of repetition can be identified
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function findPeriodOfRepetition() {
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while (true) {
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const periodOfRepetition = findRepetition(chamber.placements, (p1, p2) =>
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p1.shapeId === p2.shapeId &&
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p1.x === p2.x &&
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p1.relativeY === p2.relativeY
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);
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if (periodOfRepetition !== undefined) {
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return periodOfRepetition;
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}
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// Add 1000 rocks
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for (let i = 0; i < 1000; i++) {
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processRock();
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}
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}
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}
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const periodOfRepetition = findPeriodOfRepetition();
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let changeInHeight;
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// Confirm period of repetition
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for (let round = 0; round < 5; round++) {
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const initialHeight = chamber.height;
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// Add period of repetition rocks
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for (let i = 0; i < periodOfRepetition; i++) {
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processRock();
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}
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const change = chamber.height - initialHeight;
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if (changeInHeight === undefined) {
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changeInHeight = change;
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} else {
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if (changeInHeight !== change) {
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throw new Error(
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`Unable to confirm period of repetition, expected change in height ` +
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`of: ${changeInHeight}, got ${change}`
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);
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}
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}
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}
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const rockTarget = 1000000000000;
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const rocksRemaining = rockTarget - chamber.rockCount;
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const multiple = Math.floor(rocksRemaining / periodOfRepetition);
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const remainder = rocksRemaining % periodOfRepetition;
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// Add remaining rocks
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for (let i = 0; i < remainder; i++) {
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processRock();
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}
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const targetRockHeight = chamber.height + multiple * changeInHeight;
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console.log(
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`The tower will be: ${targetRockHeight} units tall after ${rockTarget} rocks`
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);
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