1 class Solution
2 {
3 public:
4 vector<string> result;
5 int size;
6 vector<string> letterCasePermutation(string S)
7 {
8 size = S.size();
9 DFS(S,0);
10 return result;
11 }
12 void DFS(string S,int start)
13 {
14 if(start==size)
15 {
16 result.push_back(S);
17 }
18 else
19 {
20 DFS(S,start+1);
21 string tmp_s = S;
22 if(islower(S[start]))
23 {
24 tmp_s[start] = toupper(tmp_s[start]);
25 DFS(tmp_s,start+1);
26 }
27 else if(isupper(S[start]))
28 {
29 tmp_s[start] = tolower(tmp_s[start]);
30 DFS(tmp_s,start+1);
31 }
32 }
33 }
34 };
