Given a string you need to print longest possible substring that has exactly k
unique characters. If there are more than one substring of longest possible length, return the lexicographically largest one.
"aabbcc"
and k = 1
can produce "aa"
, "bb"
and "cc"
, therefore "cc"
should be returned.
"aabbcc"
and k = 2
should return "bbcc"
.