leetcode-problemset/leetcode-cn/problem (English)/统计同构子字符串的数目(English) [count-number-of-homogenous-substrings].html

<p>Given a string <code>s</code>, return <em>the number of <strong>homogenous</strong> substrings of </em><code>s</code><em>.</em> Since the answer may be too large, return it <strong>modulo</strong> <code>10<sup>9</sup> + 7</code>.</p>



<p>A string is <strong>homogenous</strong> if all the characters of the string are the same.</p>



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



<p>&nbsp;</p>

<p><strong>Example 1:</strong></p>



<pre>

<strong>Input:</strong> s = &quot;abbcccaa&quot;

<strong>Output:</strong> 13

<strong>Explanation:</strong> The homogenous substrings are listed as below:

&quot;a&quot;   appears 3 times.

&quot;aa&quot;  appears 1 time.

&quot;b&quot;   appears 2 times.

&quot;bb&quot;  appears 1 time.

&quot;c&quot;   appears 3 times.

&quot;cc&quot;  appears 2 times.

&quot;ccc&quot; appears 1 time.

3 + 1 + 2 + 1 + 3 + 2 + 1 = 13.</pre>



<p><strong>Example 2:</strong></p>



<pre>

<strong>Input:</strong> s = &quot;xy&quot;

<strong>Output:</strong> 2

<strong>Explanation:</strong> The homogenous substrings are &quot;x&quot; and &quot;y&quot;.</pre>



<p><strong>Example 3:</strong></p>



<pre>

<strong>Input:</strong> s = &quot;zzzzz&quot;

<strong>Output:</strong> 15

</pre>



<p>&nbsp;</p>

<p><strong>Constraints:</strong></p>



<ul>

	<li><code>1 &lt;= s.length &lt;= 10<sup>5</sup></code></li>

	<li><code>s</code> consists of lowercase letters.</li>

</ul>