First_Unique_Character_in_a_String.js

// Given a string s, find the first non-repeating character in it and return its index. If it does not exist, return -1.

// Example 1:

// Input: s = "leetcode"
// Output: 0

// Example 2:

// Input: s = "loveleetcode"
// Output: 2

// Example 3:

// Input: s = "aabb"
// Output: -1

// Constraints:

//     1 <= s.length <= 105
//     s consists of only lowercase English letters.

/**
 * @param {string} s
 * @return {number}
 */
var firstUniqChar = function (s) {
  let obj = {};
  for (let key of s) obj[key] = obj[key] ? obj[key] + 1 : 1;
  for (let key of s) if (obj[key] === 1) return s.indexOf(key);
  return -1;
};