Given a string s, return the total number of substrings of s that begin and end with the same character.

A substring is a contiguous non empty sequence of characters within a string.

Constraints:

• $1 \leq$ s.length $\leq 10^5$

• s consists only of lowercase English letters.

Now, 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.