经典算法题--求对策字符串的最大长度

题目：输入一个字符串，输出该字符串对称子字符串的最大长度，如输入google，则输出4.

思路：思路很中规中矩，遍历这个字符串，若有发现相邻的两个字符相等，就循环判断与这两个字符相邻的两个字符是否相等，
   　　  直到不等，记下字符符合条件的字符个数。最大的个数即为所求。

class Program
    {
        static void Main(string[] args)
        {
            string str = "google";
            int strLen = counterplan1(str);
            Console.WriteLine(strLen);
            Console.ReadKey();

        }
        public static int counterplan1(string str)
        {
            int strlen = str.Length;
            int maxlen = 0;
            for (int i = 0; i < strlen-1; i++)
            {
                if (str[i] == str[i + 1])
                {
                    int start = i - 1;
                    int end = i + 2;
                    while (start >= 0 && end < strlen)
                    {
                        if (str[start] == str[end])
                        {
                            --start;
                            ++end;
                        }
                        else
                        {
                            break;
                        }
                    }
                    if (maxlen < end - start-1)
                    {
                        maxlen = end - start-1;
                    }
                }
               
            }
                return maxlen;
        }
    }