You are given a string s and an integer k.

Two characters in s at indices i and j with $i < j$ are considered close if they are identical and $j - i \leq k$.

As long as there exists at least one pair of close characters, repeatedly perform the following operation:

1. Find the close pair with the smallest index i. If there is a tie, choose the pair with the smallest index j.

2. Delete the character at index j from s.

Return the final string after no more operations can be performed.

Constraints:

• $1 \leq$ s.length $\leq 5 imes 10^5$

• $1 \leq$ k $\leq$ s.length

• 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.