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:
    # @param S, a string
    # @param L, a list of string
    # @return a list of integer
    def findSubstring(self, S, L):
        words = {}
        wordNum = len(L)
        for i in L:
            if i not in words:
                words[i] = 1
            else:
                words[i] += 1
        #since all words in L have same length, just count the first length
        wordLen = len(L[0])
        res = []
        for i in range(len(S)+1-wordLen*wordNum):
            curr={}
            j=0
            while j<wordNum:
                word = S[i+j*wordLen:i+j*wordLen+wordLen]
                if word not in words:
                    break
                if word not in curr:
                    curr[word]=1
                else:
                    curr[word]+=1
                if curr[word] > words[word]:
                    break
                j+=1
            if j==wordNum:
                res.append(i)
        return res