const fs = require('fs');

const INPUT_FILE = 'input-201.txt'
const OUTPUT_FILE = 'input-201.a.txt'

const file = fs.readFileSync(INPUT_FILE, 'utf8');

const array = file.split('').map(el => el).filter(el => el !== '\n');

const unmatched = [];

const _count = (arr, number) => arr.reduce((pre, cur) => (cur === number) ? ++pre : pre, 0);

const arrayFormat = arr => arr.sort().map((el) => {return {el, count: _count(arr, el)}});

const findUnPaired = final => final.filter(data => {
  if (data.count === 1) {
     return data.el
  }
});

const format = (found) => {
  if (found) {
    const lastIndex = found.slice(-1);
    if (lastIndex[0].length) {
      return lastIndex[0][0].el
    }
  }
}


const formated = arrayFormat(array);
const found = findUnPaired(formated);
unmatched.push(found);

fs.writeFile(OUTPUT_FILE, format(unmatched), function (err) {
      if (err) return console.log(err);
});