advent-of-code/2020/05/part1.js

const fs = require('fs')
const readline = require('readline');

const readInterface = readline.createInterface({
    input: fs.createReadStream('input'),
    console: false
});

let seats = []; // [[x,y], [x,y], ...]

readInterface.on('line', function(line) {
  let result = line.split('').reduce(function(sp, char) {
    const halfX = Math.floor((1 + sp[2] - sp[0]) / 2);
    const halfY = Math.floor((1 + sp[3] - sp[1]) / 2);

    switch(char) {
    case 'F': sp[3] -= halfY; break;
    case 'B': sp[1] += halfY; break;
    case 'L': sp[2] -= halfX; break;
    case 'R': sp[0] += halfX; break;
    };

    return sp;
  }, [0,0,7,127]);
  
  seats.push([result[0], result[1]]);
});

readInterface.on('close', function(line) {
  let seatIDs = seats.map((seat) => (seat[1] * 8) + seat[0]).sort((a,b) => a-b );
  console.log(seatIDs.reverse()[0]);
});