palindrome.js

const input = [
  'racecar',
  'racecarff',
  'abbccc',
  'a',
  'aabb',
  'cabc',
];

input.forEach(word => {
  // lets find all the letters we have
  const letters = {};
  [...word].forEach(letter => {
    if(!letters[letter]) letters[letter] = 0;
    letters[letter]++;
  });

  // find the middle letter and discard odd-numbered letters
  let middle = '';
  Object.keys(letters).map(letter => {
    if(letters[letter] % 2 === 1) {
      if(!middle) middle = letter;

      if(letters[letter] === 1) {        
        delete letters[letter];
      }
      else letters[letter] -= 1;      
    }
  })

  // construct the "left" part
  let result = '';
  Object.keys(letters).map(letter => {
    result += letter.repeat(letters[letter] / 2);
  })

  // right part is just left part, reversed, add middle, cook, serve, delicious
  result = `${result}${middle}${[...result].reverse().join('')}`;
  console.log(`input: ${word} longest palindrome: ${result}`);
  
})
console.log('done processing input');