【leetcode】187. Repeated DNA Sequences

题目：
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.

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思路：
笨办法，用unordered_map保存所有长度为10的substring出现的次数。

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代码实现：

class Solution {
public:
    vector<string> findRepeatedDnaSequences(string s) {
        if (s.size() < 10){
            return {};
        }
        
        vector<string> ret;
        unordered_map<string, int> my_map;
        for (int i = 0; i < s.size()-9; ++i){
            string t = s.substr(i,10);
            ++my_map[t];
            if (my_map[t] == 2){
                ret.push_back(t);
            }
        }
        
        return ret;
    }
};

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参考：
https://www.cnblogs.com/grandyang/p/4284205.html