vector<string> anagrams(vector<string> &strs) {

// IMPORTANT: Please reset any member data you declared, as

// the same Solution instance will be reused for each test case.

unordered_map<string, vector<string> > str_buf;

vector<string> ret;

if (strs.size() == 0) {

return ret;

}

// do some statistics

for (int i = 0; i < strs.size(); i++) {

string sorted = strs[i];

sort(sorted.begin(), sorted.end());

if (str_buf.count(sorted) > 0) {

str_buf[sorted].push_back(strs[i]);

} else {

str_buf.emplace(sorted, vector<string>({strs[i]}));

}

}

// push all anagrams into the output vector

for (auto it = str_buf.begin(); it != str_buf.end(); ++it) {

if (it->second.size() > 1) {

for (int i = 0; i < it->second.size(); i++) {

ret.push_back(it->second[i]);

}

}

}

return ret;

}