leetcode/work/Default/Easy/Hash Table/387.first-unique-character-in-a-string.js

/*
 * 387. First Unique Character in a String
 * Difficulty: Easy
 * https://leetcode.com/problems/first-unique-character-in-a-string/
 *
 * ──────────────────────────────────────────────────
 *
 * 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
 *
 * Explanation:
 *
 * The character 'l' at index 0 is the first character that does not
 * occur at any other index.
 *
 * Example 2:
 *
 * Input: s = "loveleetcode"
 *
 * Output: 2
 *
 * Example 3:
 *
 * Input: s = "aabb"
 *
 * Output: -1
 *
 *
 *
 * Constraints:
 *
 * 	• 1 <= s.length <= 10^5
 *
 * 	• s consists of only lowercase English letters.
 */

/**
 * @param {string} s
 * @return {number}
 */
var firstUniqChar = function (s) {
  const freq = {};
  for (let c of s) freq[c] = (freq[c] || 0) + 1;

  for (let i = 0; i < s.length; i++) {
    if (freq[s[i]] === 1) {
      return i;
    }
  }
  return -1;
};