class Solution {
public:
vector<string> letterCasePermutation(string s) {
vector<string> ans;
queue<string> qu;
qu.emplace("");
while (!qu.empty()) {
string &curr = qu.front();
if (curr.size() == s.size()) {
ans.emplace_back(curr);
qu.pop();
} else {
int pos = curr.size();
if (isalpha(s[pos])) {
string next = curr;
next.push_back(s[pos] ^ 32);
qu.emplace(next);
}
curr.push_back(s[pos]);
}
}
return ans;
}
};