Find the longest substring of a string

Given a string s, find the length of the longest substring without repeating characters.

Example 1:

Input: s = "abcabcbb"
Output: 3
Explanation: The answer is "abc", with the length of 3.

Example 2:

Input: s = "bbbbb"
Output: 1
Explanation: The answer is "b", with the length of 1.

Example 3:


Input: s = "pwwkew"
Output: 3
Explanation: The answer is "wke", with the length of 3.

Notice that the answer must be a substring, “pwke” is a subsequence and not a substring.

Constraints:

0 <= s.length <= 5 * 104

s consists of English letters, digits, symbols and spaces.

class Solution {
    
public:
    string longestSubstring(string s) {
    
            unsigned long n = s.length();

            int start = 0;
            int res = 0;
            for (int i = 0; i < n; i++) {
    
                for (int j = i; j < n; j++) {
    
                    if (checkRepetition(s, i, j)) {
    
                        if(res<j-i+1){
    
                            res = j-i+1;
                            start = i;
                        }
                    }
                }
            }

            return s.substr(start, res);
        }
        
    int lengthOfLongestSubstring(string s) {
    
        unsigned long n = s.length();

        int res = 0;
        for (int i = 0; i < n; i++) {
    
            for (int j = i; j < n; j++) {
    
                if (checkRepetition(s, i, j)) {
    
                    res = max(res, j - i + 1);
                }
            }
        }

        return res;
    }

    bool checkRepetition(string& s, int start, int end) {
    
        vector<int> chars(128);

        for (int i = start; i <= end; i++) {
    
            char c = s[i];
            chars[c]++;
            if (chars[c] > 1) {
    
                return false;
            }
        }
        return true;
    }
};


int main(int argc, const char * argv[])
{
    
    Solution s;
    string str = "123aabasdfasdfsadfasl";
    cout<<"longest Substring is:"<<s.longestSubstring(str)<<endl;
    cout<<s.lengthOfLongestSubstring(str)<<endl;
}