Given a string you need to print the size of the longest possible substring that has exactly K unique characters. If there is no possible substring then print -1.
S = "aabacbebebe", K = 3
Explanation: "cbebebe" is the longest
substring with K distinct characters.
S = "aaaa", K = 2
Explanation: There's no substring with K
You don't need to read input or print anything. Your task is to complete the function longestKSubstr() which takes the string S and an integer K as input and returns the length of the longest substring with exactly K distinct characters. If there is no substring with exactly K distinct characters then return -1.
Expected Time Complexity: O(|S|). Expected Auxiliary Space: O(1).