count-number-of-homogenous-substrings

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Algorithms

Given a string <code>s</code>, return the number of homogenous substrings of <code>s</code>. Since the answer may be too large, return it modulo <code>109 + 7</code>.

A string is homogenous if all the characters of the string are the same.

A substring is a contiguous sequence of characters within a string.

&nbsp;
Example 1:

<pre>
Input: s = &quot;abbcccaa&quot;
Output: 13
Explanation: 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>

Example 2:

<pre>
Input: s = &quot;xy&quot;
Output: 2
Explanation: The homogenous substrings are &quot;x&quot; and &quot;y&quot;.</pre>

Example 3:

<pre>
Input: s = &quot;zzzzz&quot;
Output: 15
</pre>

&nbsp;
Constraints:

<ul>
	<li><code>1 &lt;= s.length &lt;= 105</code></li>
	<li><code>s</code> consists of lowercase letters.</li>
</ul>