Longest substring Without Repeating Characters

class Solution {
public:
    int lengthOfLongestSubstring(string s) {
    int n = s.length();
    int i = 0, j = 0;
    int maxLen = 0;
    bool exist[256] = { false };
    while (j < n) {
        if (exist[s[j]]) {
            maxLen = max(maxLen, j-i);
            while (s[i] != s[j]){
                exist[s[i]] = false;
                i++;
            }
            i++;
            j++;
        } else {
            exist[s[j]] = true;
            j++;
        }
    }
    maxLen = max(maxLen, n-i);
    return maxLen;
}
};