<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;= 5 * 10<sup>5</sup></code></li>
	<li><code>s</code> consists of only lowercase English letters.</li>
</ul>

# class Solution:
#     def maximumLength(self, s: str) -> int:
#         ret = -1
#         M = {}
#         for k, v in groupby(s):
#             M.setdefault(k, []).append(len(list(v)))

#         for ch in range(26):
#             ch = chr(ord("a") + ch)
#             if ch not in M: continue

#             cnt = Counter()
#             for l in M[ch]:
#                 for i in range(l):
#                     cnt[i + 1] += l - i
#             for k in cnt:
#                 if cnt[k] >= 3:
#                     ret = max(ret, k)
                
#         return ret
class Solution:
    def maximumLength(self, s: str) -> int:

        d = defaultdict(int)
        subs = [''.join(sub) for _, sub in groupby(s)]   # <-- 1.
        
        for sub in subs:                                 #
            d[sub]+= 1                                   # <-- 2.
            if len(sub) > 1: d[sub[1:]]+= 2              #
            if len(sub) > 2: d[sub[2:]]+= 3              #

        return max(map(len,filter(lambda x: d[x] > 2,    # <-- 3.
                             d.keys())), default = -1)
                             
23100