387. 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

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.

Code

Hash

function firstUniqChar(s: string): number {
  const hash = {};

  for (let i of s) {
    if (i in hash) {
      hash[i] += 1;
    } else {
      hash[i] = 1;
    }
  }

  for (let i of s) {
    if (hash[i] == 1) {
      return s.indexOf(i);
    }
  }

  return -1;
}