<p>You are given a string <code>s</code> that consists of lowercase English letters.</p>

<p>A string is called <strong>special</strong> if it is made up of only a single character. For example, the string <code>&quot;abc&quot;</code> is not special, whereas the strings <code>&quot;ddd&quot;</code>, <code>&quot;zz&quot;</code>, and <code>&quot;f&quot;</code> are special.</p>

<p>Return <em>the length of the <strong>longest special substring</strong> of </em><code>s</code> <em>which occurs <strong>at least thrice</strong></em>, <em>or </em><code>-1</code><em> if no special substring occurs at least thrice</em>.</p>

<p>A <strong>substring</strong> is a contiguous <strong>non-empty</strong> sequence of characters within a string.</p>

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

<pre>
<strong>Input:</strong> s = &quot;aaaa&quot;
<strong>Output:</strong> 2
<strong>Explanation:</strong> The longest special substring which occurs thrice is &quot;aa&quot;: substrings &quot;<u><strong>aa</strong></u>aa&quot;, &quot;a<u><strong>aa</strong></u>a&quot;, and &quot;aa<u><strong>aa</strong></u>&quot;.
It can be shown that the maximum length achievable is 2.
</pre>

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

<pre>
<strong>Input:</strong> s = &quot;abcdef&quot;
<strong>Output:</strong> -1
<strong>Explanation:</strong> There exists no special substring which occurs at least thrice. Hence return -1.
</pre>

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

<pre>
<strong>Input:</strong> s = &quot;abcaba&quot;
<strong>Output:</strong> 1
<strong>Explanation:</strong> The longest special substring which occurs thrice is &quot;a&quot;: substrings &quot;<u><strong>a</strong></u>bcaba&quot;, &quot;abc<u><strong>a</strong></u>ba&quot;, and &quot;abcab<u><strong>a</strong></u>&quot;.
It can be shown that the maximum length achievable is 1.
</pre>

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

<ul>
	<li><code>3 &lt;= s.length &lt;= 50</code></li>
	<li><code>s</code> consists of only lowercase English letters.</li>
</ul>

class Solution:
    def maximumLength(self, s: str) -> int:     
        # Step1:
        # Time=O(N), Space=O(N)
        # two pointers to go through all repeated letter substrings (no overlap)
        counter = collections.defaultdict(int)
        l, r = 0, 1

        while r <= len(s):
            if not r == len(s) and s[l] == s[r]:
                r += 1
            else:
                substring = s[l] * (r - l)
                counter[substring] += 1
                l, r = r, r + 1

        # Step2:
        # Time=O(N), Space=O(N)
        # process substrings within substrings
        processed_counter = counter.copy()
        for key, val in counter.items():
            if len(key) > 1:
                for i in range(1, len(key)):
                    substring = key[0] * i
                    frequency = (len(key) - i + 1) * val # initial substrings are not overlapped
                    processed_counter[substring] = processed_counter.get(substring, 0) + frequency

        # Step3:
        # Time=O(N), Space=O(1)
        # Examine the processed_counter and return final answer
        max_length = -1
        for key, val in processed_counter.items():
            if val >= 3:
                max_length = max(max_length, len(key))
        
        return max_length
46