<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:
    def lengthOfLongestSubstring(self, s: str) -> int:
        if not s:
            return 0
        if len(set(s))==1:
            return 1
        
        unique=set()
        slen=0
        start=0

        for i in range(len(s)):
            while s[i] in unique:
                unique.remove(s[start])
                start+=1
            unique.add(s[i])
            slen=max(slen, i-start+1)

        return slen        

        # res=0
        # ss=''
        # for c in s:
        #     if c not in ss:
        #         ss+=c
        #         res=max(res, len(ss))
        #     else:
        #         cut=ss.index(c)
        #         ss=ss[cut+1:]+c
        # return res

        # sliding window, two pointer 
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