463. String Permutation
Kartik and Parth are both fascinated by strings. They have come up with a game where Parth gives Kartik a string and asks him to generate all possible strings in lexicographical order, starting with the smallest string. However, there is a condition that must be satisfied during the permutation process: Kartik can change each letter individually to either lowercase or uppercase, but the order of the characters in the string must remain the same.
The input consists of a single line containing a string.
Print all possible permutations of strings that satisfy the given condition.
1 <= s.length <= 12