LeetCode Repeated DNA Sequences


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.

For example,



The original problem is here.

The original code is here.

My Solution

I solve this problem in C++, as below:

*Repeated DNA Sequences
*Author: shuaijiang
*Email: zhaoshuaijiang8@gmail.com
#define Code 0x3ffff 
using namespace std;

class Solution {
    vector<string> findRepeatedDnaSequences(string s) {
        int size = s.size();
        vector<string> res;
        if(size <= 10)
            return res;
        map<int, int> myMap;
        map<char, int> char2int;
        char2int['A'] = 0;
        char2int['C'] = 1;
        char2int['G'] = 2;
        char2int['T'] = 3;
        int strInt = 0;
        for(int i=0;i<10;i++){
            strInt = (strInt << 2) + char2int[s[i]];
        myMap[strInt] = 1;
        for(int i=10; i<size; i++){
            strInt = ((strInt & Code) << 2) + char2int[s[i]];
            if(myMap.find(strInt) == myMap.end())
                myMap[strInt] = 1;
                if(myMap[strInt] == 1){
                    string substr = s.substr(i-9,10);
                myMap[strInt] ++;
        return res;


To solve the problem, use a map to save the 10-letter-long sequences and the frequence of it. Put the sequences with more than 1 frequence to the result.

However, this solution lead to ‘Memory Limit Exceeded’, to solve the problem, convert the 10-letter-long substring to an integer with ‘A’ represent ‘00’, ‘C’ represent ‘01’, ‘G’ represent ‘10’, ‘T’ represent ‘11’.