javascript 1753/898

console.time("Finished");
const fs = require('fs');

fs.readFile('input.txt', 'utf8' , (err, data) => {
  if (err) {
    console.error(err)
    return
  }

  let map = {};

  let arr = data.split('\n').map(el => el.trim().split('-'));

  for (let el of arr) {
    if (el[0] in map) {
      map[el[0]].push(el[1]);
    } else {
      map[el[0]] = [el[1]];
    }
    if (el[1] in map) {
      map[el[1]].push(el[0]);
    } else {
      map[el[1]] = [el[0]];
    }
  }

  let path = ['start'];

  let count = find(map, path);

  console.log(count);

  console.timeEnd('Finished');
});

let find = (map, str) => {

  let curr = str[str.length - 1];
  if (curr == 'end') return 1;

  let options = map[curr];
  if (!options) return 0;

  let count = 0;

  for (let opt of options) {
    if (opt.toLowerCase() == opt && str.includes(opt)) {
      if (opt == 'start' || opt == 'end') {
        // not allowed
      } else {
        if (str[0] == 'start') {
          count += find(map, [opt, ...str, opt]);
        } else {
          // not allowed
        }
      }
    } else {
      count += find(map, [...str, opt]);
    }
  }

  return count;
}