[Leetcode] Substring with Concatenation of All Words

You are given a string, S, and a list of words, L, that are all of the same length. Find all starting indices of substring(s) in S that is a concatenation of each word in L exactly once and without any intervening characters.

For example, given:
S: "barfoothefoobarman"
L: ["foo", "bar"]

You should return the indices: [0,9].

老是超时，终于过了。

class Solution {
public:
    vector<int> findSubstring(string S, vector<string> &L) {
        vector<int> res;
        if (L.size() < 1) return res;
        
        int Len = L.size() * L[0].length();
        int len = L[0].length();
        if (S.length() < Len) return res;
        
        map<string, int> word_count;
        for (int i = 0; i < L.size(); ++i) {
            word_count[L[i]]++;
        }
        map<string, int> word_detect;
        for (int i = 0; i <= S.length() - Len; ++i) {
            word_detect.clear();
            string substr;
            int j = 0;
            for (j = 0; j < Len; j += len) {
                substr = S.substr(i + j, len);
                if (word_count.find(substr) == word_count.end())
                    break;
                ++word_detect[substr];
                if (word_detect[substr] > word_count[substr])
                    break;
            }
            if (j==Len) res.push_back(i);
        }
        return res;
    }
};