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1636-number-of-substrings-with-only-1s/README.md

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+<h2><a href="https://leetcode.com/problems/number-of-substrings-with-only-1s">1636. Number of Substrings With Only 1s</a></h2><h3>Medium</h3><hr><p>Given a binary string <code>s</code>, return <em>the number of substrings with all characters</em> <code>1</code><em>&#39;s</em>. Since the answer may be too large, return it modulo <code>10<sup>9</sup> + 7</code>.</p>
+
+<p>&nbsp;</p>
+<p><strong class="example">Example 1:</strong></p>
+
+<pre>
+<strong>Input:</strong> s = &quot;0110111&quot;
+<strong>Output:</strong> 9
+<strong>Explanation:</strong> There are 9 substring in total with only 1&#39;s characters.
+&quot;1&quot; -&gt; 5 times.
+&quot;11&quot; -&gt; 3 times.
+&quot;111&quot; -&gt; 1 time.</pre>
+
+<p><strong class="example">Example 2:</strong></p>
+
+<pre>
+<strong>Input:</strong> s = &quot;101&quot;
+<strong>Output:</strong> 2
+<strong>Explanation:</strong> Substring &quot;1&quot; is shown 2 times in s.
+</pre>
+
+<p><strong class="example">Example 3:</strong></p>
+
+<pre>
+<strong>Input:</strong> s = &quot;111111&quot;
+<strong>Output:</strong> 21
+<strong>Explanation:</strong> Each substring contains only 1&#39;s characters.
+</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[i]</code> is either <code>&#39;0&#39;</code> or <code>&#39;1&#39;</code>.</li>
+</ul>