Repeated DNA Sequences

题目描述

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.

For example,

Given s = "AAAAACCCCCAAAAACCCCCCAAAAAGGGTTT",

Return:
["AAAAACCCCC", "CCCCCAAAAA"].

解题方法

原来的解法是因为A,C,G,T的ascii码只有后三位不同，所以用这后三位来区分，每次取30位，不断shift,放到hashmap里看 是否有重复的。

因为python可以用string做key,所以也可以直接用10-letter-long的字符串做key,就很简单了。

注意点

• 去掉重复的
• Index range
• 长度小于10的

Solution

class Solution(object):
    def findRepeatedDnaSequences(self, s):
        """
        :type s: str
        :rtype: List[str]
        """
        dic = {}
        length = len(s)
        result = []
        if length < 10:
            return []
        for i in range(length - 9):
            subStr = s[i:i+10]
            if subStr in dic:
                if dic[subStr] == 1:
                    result.append(subStr)
                dic[subStr] += 1
            else:
                dic[subStr] = 1

        return result

Reference

• grandyang