C# 寻找字符串中最大重复串的起始位置

例如"aabbccdeeef"，其中eee最长，返回第一个E的位置，应该为7.

        static int FindStartLargestRepeat(string str)
        {
            if (string.IsNullOrEmpty(str))
            {
                throw new Exception("Input can't be empty.");
            }

            int count = 1;
            int maxCount = 1;
            int startIndex = 0;
            for (int i = 1; i < str.Length; i++)
            {
                if (str[i]==str[i-1])
                {
                    count++;
                    if (count>maxCount)
                    {
                        maxCount = count;
                        startIndex = i - maxCount + 1;
                    }
                }
                else
                {
                    count = 1;
                }
            }
            return startIndex;
        }