leetcode 30. Substring with Concatenation of All Words

You are given a string, s, and a list of words, words, that are all of the same length. Find all starting indices of substring(s) in s that is a concatenation of each word in words exactly once and without any intervening characters.
For example, given: s:  "barfoothefoobarman" words:  ["foo", "bar"]
You should return the indices:  [0,9] . (order does not matter).

class Solution {
public:
	vector<int> findSubstring(string s, vector<string>& words) {
		vector<int>re;
		if (words.empty())
			return re;
		int wl = words[0].length();
		map<string, int>count;
		for (int i = 0; i < words.size(); i++)
			count[words[i]]++;
		int k = 0;
		while (true)
		{
			map<string, int>cnt = count;
			while (k < s.length() - wl*words.size() + 1 && cnt.find(string(s.begin() + k, s.begin() + k + wl)) == cnt.end())
				k++;
			if (k == s.length() - wl*words.size() + 1)
				return re;
			int kk = k;
			while ( !cnt.empty() && cnt.find(string(s.begin() + kk,
				s.begin() + kk + wl)) != cnt.end())
			{
				cnt[string(s.begin() + kk, s.begin() + kk + wl)]--; 
				if (cnt[string(s.begin() + kk, s.begin() + kk + wl)] == 0)
					cnt.erase(cnt.find(string(s.begin() + kk, s.begin() + kk + wl)));
				kk += wl;
			}
			if (cnt.empty())
				re.push_back(k);
			k++;
		}
		return re;
	}
};

accepted