244. Shortest Word Distance II

def __init__(self, words):
        """
        :type words: List[str]
        """
        self.d = collections.defaultdict(list)
        for i, w in enumerate(words):
            self.d[w].append(i)

    def shortest(self, word1, word2):
        """
        :type word1: str
        :type word2: str
        :rtype: int
        """
        res = float('inf')
        d1, d2, i, j = self.d[word1], self.d[word2], 0, 0
        while i < len(d1) and j < len(d2):
            res = min(res, abs(d1[i] - d2[j]))
            if d1[i] < d2[j]:
                i += 1
            else:
                j += 1
        return res