找出字符串中最大子串的长度（要求子串中的字符不重复）

给定一个字符串，找出这个字符串中的最大的子串的长度，要求这个子串中的字符不重复。下面贴出的是算法，和测试代码。

算法如下：

public Int32 GetSubCount(String str)
        {
            if (str == null)
            {
                return 0;
            }
            Int32 count = 0;
            Int32 length = count;
            String subStr = String.Empty;
            Boolean searchResult = false;
            for (Int32 item = 0; item <= str.Length-1;item++ )
            {
                searchResult = false;
                foreach (Char c in subStr)
                {
                    if (str[item] == c)
                    {
                        searchResult = true;
                        break;
                    }
                }
                if (searchResult)
                {
                    subStr = subStr.Substring(1, subStr.Length - 1);
                    count--;
                    item--;
                }
                else
                {
                    subStr += str[item].ToString();
                    count++;
                    if (count > length)
                    {
                        length = count;
                    }
                }
            }
            return length;
        }
测试代码：

[TestMethod()]
        public void GetSubCountTest()
        {
            SubString target = new SubString(); // TODO: 初始化为适当的值
            string str = string.Empty; // TODO: 初始化为适当的值
            Assert.AreEqual(0, target.GetSubCount(str));

            str = null;
            Assert.AreEqual(0, target.GetSubCount(str));

            str = "abcbec";
            Assert.AreEqual(3, target.GetSubCount(str));

            str = "abcd";
            Assert.AreEqual(4, target.GetSubCount(str));

            str = "a";
            Assert.AreEqual(1, target.GetSubCount(str));

            str = "aaaaa";
            Assert.AreEqual(1, target.GetSubCount(str));

            str = "abcdb";
            Assert.AreEqual(4, target.GetSubCount(str));

            str = "abcdd";
            Assert.AreEqual(4, target.GetSubCount(str));

            str = "abccc";
            Assert.AreEqual(3, target.GetSubCount(str));

            str = "aabccc";
            Assert.AreEqual(3, target.GetSubCount(str));
        }