784. Letter Case Permutation

Posted 2021-01-14 bernieloveslife

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.

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 between 1 and 12.
• S will consist only of letters or digits.

class Solution:
    def letterCasePermutation(self, S):
        """
        :type S: str
        :rtype: List[str]
        """
        res = set()
        def dfs(pos,s):
            if pos==len(s):
                return
            if s[pos].isalpha():
                res.add(s)
                dfs(pos+1,s)
                s = s[0:pos]+s[pos].swapcase()+s[pos+1:]
                res.add(s)
                dfs(pos+1,s)
            else:
                dfs(pos+1,s)
        dfs(0,S)
        return list(res) if len(res)>0 else [S]