Generate Different Strings

The function is given a string consisting from letters and digits. Each letter in the string can be changed to lower-case and upper-case; the digits stay as they are in their positions. Generate all possible strings and return them as set.

Examples

gen_strings("1A2") ➞ { "1A2", "1a2" }

gen_strings("a1B") ➞ { "A1B", "A1b", "a1B", "a1b" }

gen_strings("1a2bC3") ➞ { "1A2Bc3", "1a2Bc3", "1a2bC3", "1a2bc3", "1A2bC3", "1A2BC3", "1a2BC3", "1A2bc3" }

gen_strings("1") ➞ { "1" }

gen_strings("") ➞ {""}

Notes

N/A