int commonCharacterCount(string s1, string s2)
{
        if (String.IsNullOrEmpty(s1) || String.IsNullOrEmpty(s2))
                return 0;

        int[,] num = new int[s1.Length, s2.Length];
        int maxlen = 0;

        for (int i = 0; i < s1.Length; i++)
        {
                for (int j = 0; j < s2.Length; j++)
                {
                        if (s1[i] != s2[j])
                                num[i, j] = 0;
                        else
                        {
                                if ((i == 0) || (j == 0))
                                        num[i, j] = 1;
                                else
                                        num[i, j] = 1 + num[i - 1, j - 1];

                                if (num[i, j] > maxlen)
                                {
                                        maxlen = num[i, j];
                                }
                        }
                }
        }
        return maxlen;