C: string swapping to convert minimum no of characters in both the string.

Question

Input: Two strings of same length (say "ababab" "bababa")
Output: Two strings with minimum unique character used in each one ("bbbbbb" & "aaaaaa" for above example)

You can swap A[i] and B[i] for all i between 1 and N, inclusive. You cannot swap two characters within A, or within B. you can only swap a character in A with the character at the same index in B, and with no other character. You can perform this operation zero or more times.

Modify the strings through the operations in such a way that the number of unique characters in the strings is minimum.