Solution to Advent of Code 2020 Day 3 Part 1

AOC_2020_Day13_Part1.js

const fs = require('fs');
const inputParts = fs.readFileSync('day13-input.txt', 'utf-8').split('\r\n');
const earliestTimestamp = parseInt(inputParts[0].trim());

function findEarliestArrival(id) {
    let wait = id;
    while (wait < earliestTimestamp) {
        wait += id;
    }
    return wait;
}

const busses = inputParts[1].split(',').filter(id => id !== 'x' && id.length > 0).map(id => parseInt(id.trim())).map(id => ({
    id,
    earliestArrival: findEarliestArrival(id)
}));

const earliestBus = busses.reduce((earliest, current) => current.earliestArrival < earliest.earliestArrival ? current : earliest, busses[0]);
const wait = earliestBus.earliestArrival - earliestTimestamp;

console.log(`Part 1: ${ earliestBus.id * wait }`);