class Solution {
public:
/**
* @param A, B: Two string.
* @return: the length of the longest common substring.
*/
int longestCommonSubstring(string &A, string &B) {
    // write your code here
    if (A.length() > B.length()) {
        return longestCommonSubstring(B, A);
    }
    string str1, str2;
    int maxlen = 0, len = A.length();
    for (int i = 0; i < len; i++) {   //1 * len
        for (int j = 1; j <= len - i; j++) {  //
            str1 = A.substr(i, j);
            for (int m = 0; m <= B.length() - j; m++) {
                str2 = B.substr(m, j);
                if (str1 == str2) {
                    maxlen = max(maxlen, j);
                }
            }
         }
     }
return maxlen;
}