GoatLatin.js

/**
 * 824. Goat Latin
 * @param {string} S
 * @return {string}
 */
var toGoatLatin = function (S) {
  let vowel = new Set(['a', 'e', 'i', 'o', 'u', 'A', 'E', 'I', 'O', 'U']);
  S = S.split(' ');

  for (i = 0; i < S.length; i++) {
    if (vowel.has(S[i][0])) S[i] = S[i] + 'ma' + as(i + 1);
    else S[i] = S[i].slice(1, S[i].length) + S[i][0] + 'ma' + as(i + 1);
  }

  return S.join(' ');
};

function as(i) {
  let j;
  let as = '';
  for (j = 0; j < i; j++) as = as + 'a';
  return as;
}