leetcode[30]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].
(order does not matter).

class Solution {

public:

    vector<int> findSubstring(string S, vector<string> &L) {

    vector<int> res;

    int len=L[0].size()*L.size();

    if (S.empty()||L.empty()||S.size()<len)return res;

    map<string,int> Lmap;

    map<string,int> temp;

    for (int i=0;i<L.size();i++)

        Lmap[L[i]]++;

    for (int i=0;i<=(int)S.size()-len;i++)

    {

        temp.clear();

        int j=i;

        for (;j<i+len;j+=L[0].size())

        {

            string word=S.substr(j,L[0].size());

            if (Lmap.find(word)==Lmap.end())

                break;

            temp[word]++;

            if (temp[word]>Lmap[word])

                break;

        }

        if (j==i+len)

            res.push_back(i);

    }

    return res;

    }

};