Given a string <code>s</code>, return the <strong>maximum</strong> length of a <span data-keyword="substring">substring</span>&nbsp;such that it contains <em>at most two occurrences</em> of each character.
<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<div class="example-block">
<p><strong>Input:</strong> <span class="example-io">s = &quot;bcbbbcba&quot;</span></p>

<p><strong>Output:</strong> <span class="example-io">4</span></p>

<p><strong>Explanation:</strong></p>
The following substring has a length of 4 and contains at most two occurrences of each character: <code>&quot;bcbb<u>bcba</u>&quot;</code>.</div>

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

<div class="example-block">
<p><strong>Input:</strong> <span class="example-io">s = &quot;aaaa&quot;</span></p>

<p><strong>Output:</strong> <span class="example-io">2</span></p>

<p><strong>Explanation:</strong></p>
The following substring has a length of 2 and contains at most two occurrences of each character: <code>&quot;<u>aa</u>aa&quot;</code>.</div>

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

<ul>
	<li><code>2 &lt;= s.length &lt;= 100</code></li>
	<li><code>s</code> consists only of lowercase English letters.</li>
</ul>

class Solution:
    def maximumLengthSubstring(self, s: str) -> int:
        seen_ct = {}
        right = 0
        longest = 0
        left = 0
        right = 0
        while right < len(s):
            if s[right] not in seen_ct:
                seen_ct[s[right]] = 1
                longest = max(longest, right - left + 1)
            elif seen_ct[s[right]] < 2:
                seen_ct[s[right]] += 1
                longest = max(longest, right - left + 1)
            else:
                longest = max(longest, right - left)
                while left < right and seen_ct[s[right]] > 1:
                    seen_ct[s[left]] -= 1
                    if seen_ct[s[left]] <= 0:
                        seen_ct.pop(s[left])
                    left += 1
                seen_ct[s[right]] += 1
            right += 1
        # longest = max(longest, right - left)
        return longest
    
43