LeetCode 49 - Group Anagrams

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"]
]

Note:

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

My Code

class Solution {
public:
vector<vector<string>> groupAnagrams(vector<string>& strs) {
map<vector<int>, vector<string> > m;
map<vector<int>, vector<string> >::iterator it;

for (int i = 0; i < strs.size(); i++)
{
vector<int> cnts(26, 0);
for (int j = 0; j < strs[i].size(); j++)
{
cnts[strs[i][j] - 'a']++;
}
it = m.find(cnts);
if (it != m.end())
it->second.push_back(strs[i]);
else
m.insert(pair<vector<int>, vector<string> >(cnts, vector<string>(strs.begin()+i, strs.begin()+i+1)));
}

vector<vector<string> > groups;
for (it = m.begin(); it != m.end(); it++)
{
sort(it->second.begin(), it->second.end());
groups.push_back(it->second);
}

return groups;
}
};Runtime: 168 ms