Longest Common Substring

std::string LCstr(std::string &A, std::string &B)
{
    std::vector<std::vector<int>> DP(A.size() + 1, std::vector<int>(B.size() + 1, 0));
    int pos = 0, mx = 0;

    for(int i = 1; i <= A.size(); i++)
    {
        for(int j = 1; j <= B.size(); j++)
        {
            if(A[i - 1] == B[j - 1])
            {
                DP[i][j] = DP[i - 1][j - 1] + 1;

                if(DP[i][j] > mx)
                {
                    mx = DP[i][j];
                    pos = i - 1;
                }
            }
        }
    }

    return A.substr(pos - mx + 1, mx);
}