You are given a binary string s and a positive integer k.

A substring of s is considered beautiful if it contains exactly k occurrences of the character $'1'$.

Return the shortest beautiful substring of s. If there are multiple shortest beautiful substrings of the same minimum length, return the lexicographically smallest one. If no beautiful substring exists, return an empty string "".

Constraints:

• $1 \leq$ s.length $\leq 100$

• $1 \leq$ k $\leq$ s.length

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.