题目：

题解：

class Solution {const int L = 10;unordered_map<char, int> bin = {{'A', 0}, {'C', 1}, {'G', 2}, {'T', 3}};
public:vector<string> findRepeatedDnaSequences(string s) {vector<string> ans;int n = s.length();if (n <= L) {return ans;}int x = 0;for (int i = 0; i < L - 1; ++i) {x = (x << 2) | bin[s[i]];}unordered_map<int, int> cnt;for (int i = 0; i <= n - L; ++i) {x = ((x << 2) | bin[s[i + L - 1]]) & ((1 << (L * 2)) - 1);if (++cnt[x] == 2) {ans.push_back(s.substr(i, L));}}return ans;}
};