力扣-187题 重复的DNA序列（C++）- 找指定长度的目标子串+哈希

题目链接：https://leetcode-cn.com/problems/repeated-dna-sequences/
题目如下：

class Solution {
public:
    vector findRepeatedDnaSequences(string s) {
        vector result;
        int length=s.size();
        if(length<10) return result;

        unordered_map umap;
        for(int i=0;i<=length-10;++i){//注意点：i<=length-10
            string tmp=s.substr(i,10);
            umap[tmp]++;
        }

        for(auto e:umap){
            if(e.second>1) result.push_back(e.first);
        }

        return result;
    }
};