<p>You are given a string <code>word</code> and an integer <code>k</code>.</p>

<p>A substring <code>s</code> of <code>word</code> is <strong>complete</strong> if:</p>

<ul>
	<li>Each character in <code>s</code> occurs <strong>exactly</strong> <code>k</code> times.</li>
	<li>The difference between two adjacent characters is <strong>at most</strong> <code>2</code>. That is, for any two adjacent characters <code>c1</code> and <code>c2</code> in <code>s</code>, the absolute difference in their positions in the alphabet is <strong>at most</strong> <code>2</code>.</li>
</ul>

<p>Return <em>the number of <strong>complete </strong>substrings of</em> <code>word</code>.</p>

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

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

<pre>
<strong>Input:</strong> word = &quot;igigee&quot;, k = 2
<strong>Output:</strong> 3
<strong>Explanation:</strong> The complete substrings where each character appears exactly twice and the difference between adjacent characters is at most 2 are: <u><strong>igig</strong></u>ee, igig<u><strong>ee</strong></u>, <u><strong>igigee</strong></u>.
</pre>

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

<pre>
<strong>Input:</strong> word = &quot;aaabbbccc&quot;, k = 3
<strong>Output:</strong> 6
<strong>Explanation:</strong> The complete substrings where each character appears exactly three times and the difference between adjacent characters is at most 2 are: <strong><u>aaa</u></strong>bbbccc, aaa<u><strong>bbb</strong></u>ccc, aaabbb<u><strong>ccc</strong></u>, <strong><u>aaabbb</u></strong>ccc, aaa<u><strong>bbbccc</strong></u>, <u><strong>aaabbbccc</strong></u>.
</pre>

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

<ul>
	<li><code>1 &lt;= word.length &lt;= 10<sup>5</sup></code></li>
	<li><code>word</code> consists only of lowercase English letters.</li>
	<li><code>1 &lt;= k &lt;= word.length</code></li>
</ul>

class Solution:
  def countCompleteSubstrings(self, word: str, k: int) -> int:
    uniqueLetters = len(set(word))
    return sum(self._countCompleteStrings(word, k, windowSize)
               for windowSize in range(k, k * uniqueLetters + 1, k))

  def _countCompleteStrings(self, word: str, k: int, windowSize: int) -> int:
    """
    Returns the number of complete substrings of `windowSize` of `word`.
    """
    res = 0
    countLetters = 0  # the number of letters in the running substring
    count = collections.Counter()

    for i, c in enumerate(word):
      count[c] += 1
      countLetters += 1
      if i > 0 and abs(ord(c) - ord(word[i - 1])) > 2:
        count = collections.Counter()
        # Start a new substring starting at word[i].
        count[c] += 1
        countLetters = 1
      if countLetters == windowSize + 1:
        count[word[i - windowSize]] -= 1
        countLetters -= 1
      if countLetters == windowSize:
        res += all(freq == 0 or freq == k for freq in count.values())

    return res
7231