Group Anagrams

Given an array of strings, group anagrams together.

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

class Solution {
public:
    vector<vector<string> > groupAnagrams(vector<string>& strs) {
        vector<vector<string> > result;
        if(strs.empty()) return result;
        
        sort(strs.begin(), strs.end());
        unordered_map<string, vector<int> > ht;
        
        //initialize the hash table
        //sort each string and map the same into hash table
        for(int i = 0; i < strs.size(); i++){
            string temp = strs[i];
            sort(temp.begin(), temp.end());
            ht[temp].push_back(i);
        }
        
        for(unordered_map<string, vector<int> >::iterator ite = ht.begin(); ite != ht.end(); ite++){
            vector<string> temp;
            int n = (ite->second).size();
            for(int i = 0; i < n; i++){
                temp.push_back(strs[(ite->second)[i]]);
            }
            result.push_back(temp);
        }
        return result;
    }
};

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

Note:

1. For the return value, each inner list's elements must follow the lexicographic order.
2. All inputs will be in lower-case.

Update (2015-08-09):
The signature of the function had been updated to return list<list<string>> instead of list<string>, as suggested here. If you still see your function signature return a list<string>, please click the reload button  to reset your code definition.