leetcode187

class Solution:
    def findRepeatedDnaSequences(self, s: str) -> 'List[str]':
        n = len(s)
        if n <= 10:
            return []
        res = []
        bstr = s[:10]
        dic = {bstr:1}
        i,j = 1,10
        while j < n:
            nstr = bstr[1:] + s[j]
            if nstr not in dic:
                dic[nstr] = 1
            else:
                dic[nstr] += 1
            j += 1
            bstr = nstr
        for k,v in dic.items():
            if v > 1:
                res.append(k)
        return res