【leetcode】187. Repeated DNA Sequences

题目如下：

All DNA is composed of a series of nucleotides abbreviated as A, C, G, and T, for example: "ACGAATTCCG". When studying DNA, it is sometimes useful to identify repeated sequences within the DNA.

Write a function to find all the 10-letter-long sequences (substrings) that occur more than once in a DNA molecule.

Example:

Input: s = "AAAAACCCCCAAAAACCCCCCAAAAAGGGTTT"

Output: ["AAAAACCCCC", "CCCCCAAAAA"]

解题思路：题目本身很简单，依次判断每个子串s[i:i+10]是否重复即可。

代码如下：

class Solution(object):
    def findRepeatedDnaSequences(self, s):
        """
        :type s: str
        :rtype: List[str]
        """
        dic = {}
        end = 10
        substring = s[:end]
        dic[substring] = end - 1
        res = []
        while end < len(s):
            substring = substring[1:] + s[end]
            end += 1
            if substring in dic:
                if dic[substring] == -1:
                    continue
                res.append(substring)
                dic[substring] = -1
            else:
                dic[substring] = end - 1

        return res