leetcode 3 无重复的最大子列

class Solution 
{
public:
    int lengthOfLongestSubstring(string s) 
    {
        int sign = 0;
        int j = 1;
        int max = 0;
        for(int i = 0 ; s[i] ; i++)
        {
            for(j = 1 ; s[i+j] ; j++)
            {
                for(int k = 0 ; k<j ; k++)
                {
                    if(s[i+j] == s[i+k])
                    {
                        sign = 1;
                        break;  
                    }

                }
                if(sign)
                {
                    sign = 0;
                    break;
                }
            }
            if(max<j)
            max = j;            //执行到这里，说明该开头已经检查完毕
        }
        return max;
    }
};

class Solution 
{
public:
    int lengthOfLongestSubstring(string s) 
    {
        unordered_set<char> occ;
        int n = size(s);
        int i = -1;
        int j = 0;
        int maxSize = 0;
        for(i = 0 ; i < n ; i++)
        {
            if(i)
            {
                occ.erase(s[i-1]);
            }
            while(j<n && !occ.count(s[j]))
            {
                occ.insert(s[j]);
                j++;
            }
            maxSize = max(maxSize,j-i);
        }
        return maxSize;
    }
};