最长无重复字符子串长度

题目：Given a string, find the length of the longest substring without repeating characters. For example, the longest substring without repeating letters for "abcabcbb" is "abc", which the length is 3. For "bbbbb" the longest substring is "b", with the length of 1.
分析：从头开始记录每个字母出现次数，如果出现过则计算目前子串长度，并从此处开始新的子串检测。
参考链接：http://blog.csdn.net/ojshilu/article/details/12168533
代码：

#include <iostream>

using namespace std;

class Test
{
    public:
        int exsit_status[30] ;

        bool IsExisit(char alp)
        {
            if ( (alp >= 'a') && (alp<= 'z') )
            {
                if (exsit_status[alp - 'a'] == 0)
                    return false;
                else
                    return true;
            }
        }
        void addStatus(char alp)
        {
            if ( (alp >= 'a') && (alp<= 'z') )
            {
               exsit_status[alp - 'a'] = 1;
            }
        }
        void clearStatus()
        {
            char alp;
            for (alp='a'; alp<='z'; alp++)
            {
                exsit_status[alp-'a'] = 0;
            }
        }
        int LongestSubstr(string str)
        {
            if (str == "")
                return 0;

            int len = str.length();
            int max_len = 0;
            int i,j;

            clearStatus();
            for (i=0; i<len; i++)
            {
                for (j=i; j<len; j++)
                {
                    if ( IsExisit(str[j]) == true )
                    {
                        if (max_len < j-i)
                        {
                            max_len = j-i;
                        }
                        clearStatus();
                        i = j-1;
                        break;
                    }
                    else
                    {
                        addStatus(str[j]);
                    }
                }
                if (max_len < j-i)
                {
                    max_len = j-i;
                    break;
                }
            }
            return max_len;
        }
};


int main()
{
    class Test my_test;
    cout<<my_test.LongestSubstr("abcdcabc")<<endl;
    return 0;
}