LintCode 774: Repeated DNA

774. Repeated DNA

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.

Example
Example 1:

Input:
“AAAAACCCCCAAAAACCCCCCAAAAAGGGTTT”
Output:
[“AAAAACCCCC”,“CCCCCAAAAA”]
Example 2:

Input:
“GAGAGAGAGAGA”
Output:
[“GAGAGAGAGA”]

解法1：

class Solution {
public:
    /**
     * @param s: a string represent DNA sequences
     * @return: all the 10-letter-long sequences 
     */
    vector<string> findRepeatedDna(string &s) {
        int n = s.size();
        if (n < 10) return vector<string>();
        unordered_map<string, int> strMap;
        vector<string> result;
        
        for (int i = 10; i <= n; ++i) {
            string subString = s.substr(i - 10, 10);
            strMap[subString]++;
        }
        
        for (auto elem : strMap) {
            if (elem.second > 1) result.push_back(elem.first);
        }
        return result;
    }
};