LeetCode Repeated DNA Sequences的一点疑惑

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"].

Solution:

vector<string> findRepeatedDnaSequences(string s) {

map<int, int> m;
vector<string> r;
int t = 0, i = 0, ss = s.size();
while (i < 9)
t = t << 3 | s[i++] & 7; //该行获取A C G T中ASCII码的末位数值 通过末位判断更节省空间
while (i < ss)
if (m[t = t << 3 & 0x3FFFFFFF | s[i++] & 7]++ == 1)
r.push_back(s.substr(i - 10, 10));
return r;

}

对这个算法还没有正确理解,求大神指导

自问自答:

理解了,通过哈希表记录每个可能的字符串(已经处理过的只有ASCII码的后三位),出现一次就对应哈希值就自加一次 如果出现超过两次的就加入到r数组当中.