Advent of Code 2020, Day 5 TypeScript (functional style)

AoC-2020-day5.ts

// Advent of code 2020, Day 5

import fs from 'fs';
import assert from 'assert';

function convertStringToSeatId(seatCode: string): number {
	return (Array.prototype.map.call(seatCode, (c: string): number => {
		switch (c) {
			case 'F':
			case 'L':
				return 0;
			case 'B':
			case 'R':
				return 1;
			default:
				throw new Error(`Invalid character '${c}' in "${seatCode}"`);
		}
	}) as number[]).reduce((a: number, b: number) => a * 2 + b);
}

const TestCases: [string, number, number, number][] = [
	['FBFBBFFRLR', 44, 5, 357], // Part 1
	['BFFFBBFRRR', 70, 7, 567],
	['FFFBBBFRRR', 14, 7, 119],
	['BBFFBBFRLL', 102, 4, 820],
];

for (const tc of TestCases) {
	const seatId = convertStringToSeatId(tc[0]);
	assert(seatId === tc[3], tc[0]);
}

// Question says not first or last row
const SeatMin = 8,
	SeatMax = 8 * 126;

// Skip after finding one since we're only looking for 1 seat
let foundOne = false;

// Go!
const seats = fs
	.readFileSync('data/AoC-Day-5-data.txt', 'utf-8')
	// Split it up
	.split(/[\n\r]/g)
	// Remove blank lines (especially trailing)
	.filter((s) => 0 < s.length)
	// Convert to seat Ids
	.map(convertStringToSeatId)
	// Sort needs telling not to use char codes!?
	.sort((a, b) => a - b)
	// Find the one matching the question rule
	.filter((id, index, seats) => {
		if (foundOne || id < SeatMin || id > SeatMax) return false;
		// Use Hannah Rose's (and others') fantastic observation about there being a gap in the sorted seat list
		foundOne = 2 === seats[index + 1] - id;
		return foundOne;
	});

console.log(`seats:${seats.length}:\n`, seats);