Group Anagrams

Given an array of strings, group anagrams together.

For example, given: ["eat", "tea", "tan", "ate", "nat", "bat"], 
Return:

[  ["ate", "eat","tea"],  ["nat","tan"],  ["bat"]]

class Solution {public:    vector<vector<string>> groupAnagrams(vector<string>& strs) {        vector<vector<string> > res;        unordered_map<string,vector<string> > m;                for(int i=0;i<strs.size();i++)        {            string t=strs[i];            sort(t.begin(),t.end());                        m[t].push_back(strs[i]);        }               unordered_map<string,vector<string> >::iterator it=m.begin();       while(it != m.end())       {           res.push_back(it->second);           it++;       }       return res;    }};