Algorithm

We can start by examining every possible substring of the input string and check whether it contains at most k distinct characters. If it does, we record its length and keep track of the maximum length found so far.

Loop over all possible starting indices of substrings.
For each starting index, loop over all possible ending indices till the end of the string.
For each such substring, track the number of distinct characters using a set or frequency map.
If the number of distinct characters is less than or equal to the given limit, update the maximum length found so far.
After checking all substrings, return the maximum valid length obtained.