group anagrams

https://leetcode.com/problems/anagrams/

class Solution {
public:
    vector<vector<string>> groupAnagrams(vector<string>& strs) {
        vector<vector<string>> rst;
        if(strs.size() == 0)
        {
            return rst;
        }

        map<string, vector<string>> hash;
        for(string str : strs)
        {
            string org = str;
            sort(str.begin(), str.end());
            hash[str].push_back(org);
        }

        for(auto& kv : hash)
        {
            rst.push_back(kv.second);
        }

        return rst;
    }
};