new_contents: class Solution(object):
      def findRepeatedDnaSequences(self, s):
          """
          :type s: str
          :rtype: List[str]
          """
          L = 10
          if len(s) <= L:
              return []
          
          counter = {}
          m = {'A': 0, 'C': 1, 'G': 2, 'T': 3}
          value = 0
          for i in range(L):
              value = 4 * value + m[s[i]]
          counter[value] = 1
          
          ret = []
          for i in range(L, len(s)):
              value = (value - pow(4, L - 1) * m[s[i - L]]) * 4 + m[s[i]]
              counter[value] = counter.get(value, 0) + 1
              if counter[value] == 2:
                  ret.append(s[i - 9:i + 1])
                      
          return ret
              
          
subject: add repeated-dna-sequences