int longestCommonSubstring(string &A, string &B) {
    // write your code here
    if(A.length() == 0 || B.length() == 0) {
        return 0;
    }

    int lcs = 0, cs = 0;
    for(unsigned i=0; i<A.length(); i++) {
        for(unsigned j=0; j<B.length(); j++) {
            cs = 0;
            while(i+cs < A.length() && j+cs < B.length() && A[i+cs] == B[j+cs]) {
                cs += 1;
            }
            lcs = max(lcs, cs);
        }
    }

    return lcs;
}