# 0387. First Unique Character in a String

<https://leetcode.com/problems/first-unique-character-in-a-string>

## Description

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.

## ac

```java
class Solution {
    public int firstUniqChar(String s) {
        // edge case
        if (s == null || s.length() == 0) return -1;

        int[] note = new int[26];
        for (int i = 0; i < s.length(); i++) {
            note[s.charAt(i) - 'a']++;
        }
        for (int i = 0; i < s.length(); i++) {
            if (note[s.charAt(i) - 'a'] == 1) {
                return i;
            }
        }

        return -1;
    }
}
```