FirstUniqueCharacterInAString.js

/**
 * 387. First Unique Character in a String
 * @param {string} s
 * @return {number}
 */
var firstUniqChar = function (s) {
  let collection = new Set();
  let repeat = new Set();
  for (i = 0; i < s.length; i++) {
    if (!collection.has(s[i])) collection.add(s[i]);
    else repeat.add(s[i]);
  }
  for (i = 0; i < s.length; i++)
    if (!repeat.has(s[i])) return i;
  return -1;
};