Given a string s, return the lexicographically smallest subsequence of s that contains every distinct character of s exactly once.

Note: This question is the same as LeetCode $316$.

Constraints:

• $1 \leq$ s.length $\leq 1000$

• s consists 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.