longest substring without repeating character leetcode c++

this problem broaden its test set,so that we should use sign[xxxx]-'a' two record;

and when we calculate the length, we should test j-i+1;

class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        
    int sign[300]={0};
    int i = 0;
    int j = 0;
    int max = 0;
    for(i = 0,j = 0;j<s.length();j++)
    {
        while(sign[s[j]-' '] == 1)
            {
                sign[s[i]-' '] = 0;
                i++;
            }
         sign[s[j]-' '] = 1;
        if(j-i +1> max)
            max = j-i+1;
    }
    return max;   
    }
};