网址:https://leetcode.com/problems/letter-case-permutation/
basic backtracking
class Solution {
public:
void backTrack(string s, string res, int i, vector<string> &ans)
{
if (i == s.size())
{
ans.push_back(res);
return;
}
if (!isalpha(s[i]))
backTrack(s, res + s[i], i + , ans);
else
{
backTrack(s, res + (char)tolower(s[i]), i + , ans);
backTrack(s, res + (char)toupper(s[i]), i + , ans);
}
}vector<string> letterCasePermutation(string S)
{
vector<string> ans;
string res;
backTrack(S, res, , ans);
return ans;
}
};