For a given string of characters, s, your task is to find the first non-repeating character and return its index. Return $-1$ if there’s no unique character in the given string.

Constraints:

• $1 \leq$ s.length $\leq 10^{3}$
• Only lowercase English letters are accepted.
• There are no spaces in the string.

Let’s take a moment to make sure you’ve correctly understood the problem. The quiz below helps you check if you’re solving the correct problem:

We have a game for you to play. Rearrange the logical building blocks to develop a clearer understanding of how to solve this problem.

Implement your solution in the following coding playground.