【Anagrams】 cpp

class Solution {
public:
    vector<string> anagrams(vector<string>& strs) {
        vector<string> ret;
        map<string,vector<int> > str_indexs;
        // trans strs to key (sorted string) and value (indexs of strs that have same key) pairs
        for ( size_t i = 0; i < strs.size(); ++i )
        {
            string key = strs[i];
            std::sort(key.begin(), key.end());
            str_indexs[key].push_back(i);
        }
        // add the keys which occurs more than once
        for ( map<string,vector<int> >::iterator it = str_indexs.begin(); it!= str_indexs.end(); ++it )
        {
            if ( it->second.size()>1 )
            {
                for ( size_t k = 0; k < it->second.size(); ++k )
                {
                    ret.push_back(strs[it->second[k]]);
                }
            }
        }
        return ret;
    }
};