784. Letter Case Permutation

Medium

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Given a string s, we can transform every letter individually to be lowercase or uppercase to create another string.

Return a list of all possible strings we could create. You can return the output in any order.

Example 1:

Input: s = "a1b2"
Output: ["a1b2","a1B2","A1b2","A1B2"]

Example 2:

Input: s = "3z4"
Output: ["3z4","3Z4"]

Example 3:

Input: s = "12345"
Output: ["12345"]

Example 4:

Input: s = "0"
Output: ["0"]

Constraints:

• s will be a string with length between 1 and 12.

• s will consist only of letters or digits.

class Solution:
    def letterCasePermutation(self, s: str) -> List[str]:
        s = s.lower()
        result = set()
        def recursion(s, ele, start, result):
            if start >= len(s):
                result.add(ele)
                return
            for index in range(start, len(s)):
                recursion(s, ele[:index] + ele[index].upper() + ele[index+1:], index+1, result)
                recursion(s, ele, index+1, result)
        recursion(s,s,0, result)
        return list(result)