187. Repeated DNA Sequences 【M】【30】

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本文介绍了一种使用Python实现的方法，该方法能够找出DNA序列中长度为10且出现次数超过一次的所有子序列。通过构建一个字典来跟踪所有可能的子序列及其出现频率，最终筛选出符合要求的重复序列。

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"].

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从头到尾顺序扫描的hash

class Solution(object):
    def findRepeatedDnaSequences(self, s):
        
        dic = {}
        
        for i in xrange(len(s) - 9):
            t = s[i:i+10]
            
            dic[t] = dic.get(t,0) + 1
        
        #l = sorted(dic.iteritems(),key = lambda d:d[1],reverse = True)
        res = []
        
        for k,v in dic.items():
            #print k,v
            if v > 1:
                res += k,
                
        #print res
        return res
        
        """
        :type s: str
        :rtype: List[str]
        """