First Unique Character in a String

## 🔠 First Unique Character in a String

Problem Statement:
Given a string s, return the index of the first non-repeating character.
If there is no such character, return -1.

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### Example 1

Input:


s = "leetcode"


Output:


0


Explanation:
The character 'l' appears only once and is the first unique character.

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### Example 2

Input:


s = "loveleetcode"


Output:


2


Explanation:
The character 'v' is the first non-repeating character.

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### Example 3

Input:


s = "aabb"


Output:


-1


Explanation:
All characters repeat, so there is no unique character.

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### Constraints

* 1 ≤ s.length ≤ 10⁵
* s consists of lowercase English letters only