Code Golf: Longest 3-character substring
Write a function called burrito that takes in a string and returns a contiguous substring within that string. This substring should be the longest possible substring that contains at most 3 unique characters.
>>> burrito("a b c b a")
" b c b "
Note that the string can contain any type of character, not just letters.
If there is a tie, you can return any valid answer (no verification tests will have ambiguous input)
The string will always be non-empty