<p>Given a string <code>s</code>, find the length of the <strong>longest</strong> <span data-keyword="substring-nonempty"><strong>substring</strong></span> without repeating characters.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;abcabcbb&quot;
<strong>Output:</strong> 3
<strong>Explanation:</strong> The answer is &quot;abc&quot;, with the length of 3.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;bbbbb&quot;
<strong>Output:</strong> 1
<strong>Explanation:</strong> The answer is &quot;b&quot;, with the length of 1.
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;pwwkew&quot;
<strong>Output:</strong> 3
<strong>Explanation:</strong> The answer is &quot;wke&quot;, with the length of 3.
Notice that the answer must be a substring, &quot;pwke&quot; is a subsequence and not a substring.
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>0 &lt;= s.length &lt;= 5 * 10<sup>4</sup></code></li>
	<li><code>s</code> consists of English letters, digits, symbols and spaces.</li>
</ul>

class Solution {
public:
    int helper(string &s,int start,int end){
        for(int i = start;i<=end;i++){
            if(s[i] == s[end+1]){
                return i;
            }
        }
        return -1;
    }
    string solver(string &s, int start) {
        string ans = "";
        int maxLength = 0;
        string longestSubstring = "";

        for (int i = start; i < s.length(); i++) {
            int help = helper(s, start, i - 1);
            if (help == -1) {
                ans += s[i];
                if (ans.length() > maxLength) {
                    maxLength = ans.length();
                    longestSubstring = ans;  // Keep track of the longest 
                    //substring
                }
            } else {
                string candidate = solver(s, help + 1);
                if (candidate.length() > longestSubstring.length()) {
                    longestSubstring = candidate;
                }
                break; 
            }
        }
        return longestSubstring;
    }
    int lengthOfLongestSubstring(string s) {
        string ans = solver(s,0);
        return ans.length();
    }
};
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