<p>You are given a string <code>s</code> and an array of strings <code>words</code> of <strong>the same length</strong>. Return&nbsp;all starting indices of substring(s) in <code>s</code>&nbsp;that is a concatenation of each word in <code>words</code> <strong>exactly once</strong>, <strong>in any order</strong>,&nbsp;and <strong>without any intervening characters</strong>.</p>

<p>You can return the answer in <strong>any order</strong>.</p>

<p>&nbsp;</p>
<p><strong>Example 1:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;barfoothefoobarman&quot;, words = [&quot;foo&quot;,&quot;bar&quot;]
<strong>Output:</strong> [0,9]
<strong>Explanation:</strong> Substrings starting at index 0 and 9 are &quot;barfoo&quot; and &quot;foobar&quot; respectively.
The output order does not matter, returning [9,0] is fine too.
</pre>

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

<pre>
<strong>Input:</strong> s = &quot;wordgoodgoodgoodbestword&quot;, words = [&quot;word&quot;,&quot;good&quot;,&quot;best&quot;,&quot;word&quot;]
<strong>Output:</strong> []
</pre>

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

<pre>
<strong>Input:</strong> s = &quot;barfoofoobarthefoobarman&quot;, words = [&quot;bar&quot;,&quot;foo&quot;,&quot;the&quot;]
<strong>Output:</strong> [6,9,12]
</pre>

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

<ul>
	<li><code>1 &lt;= s.length &lt;= 10<sup>4</sup></code></li>
	<li><code>s</code> consists of lower-case English letters.</li>
	<li><code>1 &lt;= words.length &lt;= 5000</code></li>
	<li><code>1 &lt;= words[i].length &lt;= 30</code></li>
	<li><code>words[i]</code>&nbsp;consists of lower-case English letters.</li>
</ul>