784. Letter Case Permutation

Posted 2020-10-26 __Meng

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 at most 12.
• S will consist only of letters or digits.

 

将S的每个字母进行大写小小写转换，求出所有的可能

 

 

C++（9ms）：  BFS

 1 class Solution {
 2 public:
 3     vector<string> letterCasePermutation(string S) {
 4         queue<string> que ;
 5         que.push(S) ;
 6         for(int i = 0 ; i < S.size() ; i++){
 7             if (isdigit(S[i]))
 8                 continue ;
 9             int len = que.size() ;
10             for (int j = 0 ; j < len ; j++){
11                 string cur = que.front() ;
12                 que.pop() ;
13                 
14                 cur[i] = toupper(cur[i]);
15                 que.push(cur) ;
16                 
17                 cur[i] = tolower(cur[i]) ;
18                 que.push(cur) ;
19             }
20         }
21         vector<string> res ;
22         int len = que.size() ;
23         for(int i = 0 ; i < len ; i++){
24             res.push_back(que.front()) ;
25             que.pop() ;
26         }
27         return res ;
28     }
29 };