30. Substring with Concatenation of All Words leetcode Python 2016 new season

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 wordsexactly 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).

it will take O(n) space and O(kmn) time n is s length k is word length m is words length

class Solution(object):
    def findSubstring(self, s, words):
        """
        :type s: str
        :type words: List[str]
        :rtype: List[int]
        """
        result = []
        if not words:
            return result
        word_length = len(words[0])
        words_length = len(words)
        s_length = len(s)
        word_hash = {}
        for word in words:
            if word in word_hash:
                word_hash[word] += 1
            else:
                word_hash[word] = 1
    
        for index in range(word_length):
            left_index = index
            count = 0
            sub_hash = {}
            # sliding window
            for slide_index in xrange(index, s_length - word_length + 1, word_length):
                new_word = s[slide_index : slide_index + word_length]
                #check valid word
                if new_word in word_hash:
                    if new_word in sub_hash:
                        sub_hash[new_word]  += 1
                    else:
                        sub_hash[new_word] = 1
                    count += 1
                    # move index to first none duplicate word
                    #"wordgoodgoodgoodbestword"
                    # ["word","good","best","good"] move to  index 8 instead of 4
                    while sub_hash[new_word] > word_hash[new_word]:
                        sub_hash[s[left_index:left_index + word_length]] -= 1
                        count -= 1
                        left_index += word_length
                    if count == words_length:
                        result.append(left_index)
                else:
                    count = 0
                    sub_hash = {}
                    left_index = slide_index + word_length
        return result