import fs from "fs"; const EMPTY = "L"; const OCCUPIED = "#"; const FLOOR = "."; class Field { /** * @param {string[][]} lines Lines of the field */ constructor(lines) { this.lines = lines; } toString() { return this.lines.map((line) => line.join("")).join("\n"); } get occupiedSeatCount() { return this.lines.reduce( (result, line) => result + line.filter((val) => val === OCCUPIED).length, 0 ); } /** * Checks visible seats from a given position * * @param {number} x X-Coordinate of the seat to check * @param {number} y Y-Coordinate of the seat to check * @returns {Promise} Amount of seats visible from the given position */ checkVisibleSeats(x, y) { let occupiedNeighbors = 0; for (let dY = -1; dY <= 1; dY++) { const curLine = this.lines[y + dY]; if (curLine === undefined) continue; for (let dX = -1; dX <= 1; dX++) { if (dX === 0 && dY === 0) continue; const curCell = curLine[x + dX]; if (curCell === OCCUPIED) occupiedNeighbors++; } } return occupiedNeighbors; } /** * @returns {number} Amount of seats that changed states. */ step() { let changes = 0; /** @type {string[][]} */ const changedLines = JSON.parse(JSON.stringify(this.lines)); for (let y = 0; y < this.lines.length; y++) { for (let x = 0; x < this.lines[y].length; x++) { const currentCell = this.lines[y][x]; if (currentCell === FLOOR) continue; const occupiedNeighbors = this.checkVisibleSeats(x, y); if (currentCell === EMPTY && occupiedNeighbors === 0) { changedLines[y][x] = OCCUPIED; changes++; } else if (currentCell === OCCUPIED && occupiedNeighbors >= 4) { changedLines[y][x] = EMPTY; changes++; } } } this.lines = changedLines; return changes; } } /** * Main function for Puzzle A * * @param {string} data - Puzzle input as a single string. * @returns {number} Amount of open seats after applying all rules until stable. */ async function main(data) { const lines = data.split(/\r?\n/).map((line) => line.split("")); const field = new Field(lines); let steps = 0; while (field.step() > 0) { // console.log("Step", ++steps); } return field.occupiedSeatCount; } fs.readFile("input", (err, data) => { if (err) throw err; main(data.toString()).then(console.log).catch(console.error); });