---
title: LC-387
description: First Unique Character in a String
---

## Examples

| Input            | Output |
| ---------------- | ------ |
| `"leetcode"`     | `0`    |
| `"loveleetcode"` | `2`    |
| `"aabb"`         | `-1`   |

## Hints

<Accordion type="single">
  <AccordionItem title="Constraints">
    Constraints:
     • `1 <= s.length <= 10^5`
     • `s` consists of only lowercase English letters.
  </AccordionItem>
  <AccordionItem title="Problem Statement">
    Given a string `s`, find the first non-repeating character in it and return its index.
    If it does not exist, return `-1`.
  </AccordionItem>
</Accordion>

## Solution

```js
/**
 * @param {string} s
 * @return {number}
 */

var firstUniqChar = function (s) {
  // Default for Hammer
  const freq = {};
  for (let c of s) freq[c] = (freq[c] || 0) + 1;

  // Problem Specific
  // Loop the ORIGINAL string — we want an index, so no sorting
  for (let i = 0; i < s.length; i++) {
    if (freq[s[i]] === 1) {
      return i;
    }
  }
  return -1;
};
```