Repeated DNA Sequences问题及解法

问题描述：

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.

示例：

Given s = "AAAAACCCCCAAAAACCCCCCAAAAAGGGTTT",Return:["AAAAACCCCC", "CCCCCAAAAA"].

问题分析：

每次取长度为10的子串，判断是否出现过或者出现次数2次及以上，两次以上的保留到结果集上。

过程详见代码：

class Solution {public:    vector<string> findRepeatedDnaSequences(string s) {        vector<string> res;unordered_map <string, int> m;for (int i = 0; i + 9 < s.length();i++){string str = s.substr(i, 10);if (!m.count(str)) m[str] = 1;else m[str]++;}for (auto ms : m){if (ms.second > 1) res.emplace_back(ms.first);}return res;    }};