[LeetCode] Challenge log 784

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784. Letter Case Permutation

Recursive solution.

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.

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

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

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

Note:

  • S will be a string with length at most 12.
  • S will consist only of letters or digits.
Soulution:
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class Solution:
    def letterCasePermutation(self, S):
        """
        :type S: str
        :rtype: List[str]
        """
        if S == '': return ['']
        rest = self.letterCasePermutation(S[1:])
        if 65 <= ord(S[0]) <= 122:
            return [S[0].lower() + x for x in rest] + [S[0].upper() + x for x in rest]
        else:
            return [S[0] + x for x in rest]
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