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

async function processLineByLine() {
    const fileStream = fs.createReadStream('login'); // data is copied and pasted into a file called 'login'

    const rl = readline.createInterface({
      input: fileStream,
      crlfDelay: Infinity
    });

    let charOrders = {};

    for await (const line of rl) {
      const chars = [...line.trim()]
      if (chars.length !== 3) {
          throw new Error('chars not of size 3');
      }

      // build charOrders such that each key is a letter of the password that maps to a set of all the letters after it

      addMapping(charOrders, chars[0], chars[1]);
      addMapping(charOrders, chars[0], chars[2]);
      addMapping(charOrders, chars[1], chars[2]);
      addMapping(charOrders, chars[2], null);
    }

    // the size of the list corresponds (inversely) to the index of the the password

    const pass = new Array(1000)
    for (let [key, val] of Object.entries(charOrders)) {
        if (val.has(null)) {
            val.delete(null)
        }

        pass[1000-val.size-1] = key;
    }
    console.log(pass.join(""));
}
processLineByLine()

function addMapping(dest, key, val) {
    if (!dest.hasOwnProperty(key)) {
        dest[key] = new Set();
    }
    dest[key].add(val);
}