【LeetCode】187. Repeated DNA Sequences

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"].

每个长度为10的字符串，通过查找map，判断之前是否出现过。

用hash可以降低空间复杂度。

class Solution {
public:
    vector<string> findRepeatedDnaSequences(string s) {
        vector<string> ret;
        if(s.size() < 10)
            return ret;
        unordered_map<size_t, int> m;
        hash<string> strh;

        for(int i = 0; i <= s.size()-10; i ++)
        {
            string sub = s.substr(i, 10);
            m[strh(sub)] ++;
            if(m[strh(sub)] == 2)
            {//find repeat
                ret.push_back(sub);
            }
        }
        return ret;
    }
};