187. Repeated DNA Sequences

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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每个基因可以用两位表示

A:00 ->1

B:01 ->1

G::10 ->2

T:11 ->3

10个字符可以2^20种表达形式2^20<2^32,所以可以用int来存放。

class Solution {
public:
    vector findRepeatedDnaSequences(string s) {
        vector res;
        int len=s.size();
        if(len<10) return res;
        map m;
        for(int i=0;i<=len-10;i++){
            string sub=s.substr(i,10);
            int code=encode(sub);
            if(m.count(code)){
                if(m[code]==1) res.push_back(sub);
                m[code]++;
            }else{
                m[code]++;
            }
        }
        return res;
    }
private:
    int encode(string sub){
        int code=0;
        for(int i=0;i