难度: Easy
原题连接
内容描述
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.
思路 1 - 时间复杂度: O(2^N)- 空间复杂度: O(1)******
很简单的dfs, beats 45.03%
class Solution:
def letterCasePermutation(self, S):
"""
:type S: str
:rtype: List[str]
"""
def dfs(s, idx):
if idx == len(s):
return
dfs(s, idx+1)
if not s[idx].isdigit():
if ord(s[idx]) <= ord('Z'):
self.res.add(s[:idx]+s[idx].lower()+s[idx+1:])
dfs(s[:idx]+s[idx].lower()+s[idx+1:], idx+1)
else:
self.res.add(s[:idx]+s[idx].upper()+s[idx+1:])
dfs(s[:idx]+s[idx].upper()+s[idx+1:], idx+1)
if not S or len(S) == 0:
return ['']
self.res = set([S])
dfs(S, 0)
return list(self.res)