leetcode-problemset/leetcode/problem/count-number-of-texts.html

<p>Alice is texting Bob using her phone. The <strong>mapping</strong> of digits to letters is shown in the figure below.</p>
<img alt="" src="https://assets.leetcode.com/uploads/2022/03/15/1200px-telephone-keypad2svg.png" style="width: 200px; height: 162px;" />
<p>In order to <strong>add</strong> a letter, Alice has to <strong>press</strong> the key of the corresponding digit <code>i</code> times, where <code>i</code> is the position of the letter in the key.</p>

<ul>
	<li>For example, to add the letter <code>&#39;s&#39;</code>, Alice has to press <code>&#39;7&#39;</code> four times. Similarly, to add the letter <code>&#39;k&#39;</code>, Alice has to press <code>&#39;5&#39;</code> twice.</li>
	<li>Note that the digits <code>&#39;0&#39;</code> and <code>&#39;1&#39;</code> do not map to any letters, so Alice <strong>does not</strong> use them.</li>
</ul>

<p>However, due to an error in transmission, Bob did not receive Alice&#39;s text message but received a <strong>string of pressed keys</strong> instead.</p>

<ul>
	<li>For example, when Alice sent the message <code>&quot;bob&quot;</code>, Bob received the string <code>&quot;2266622&quot;</code>.</li>
</ul>

<p>Given a string <code>pressedKeys</code> representing the string received by Bob, return <em>the <strong>total number of possible text messages</strong> Alice could have sent</em>.</p>

<p>Since the answer may be very large, return it <strong>modulo</strong> <code>10<sup>9</sup> + 7</code>.</p>

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

<pre>
<strong>Input:</strong> pressedKeys = &quot;22233&quot;
<strong>Output:</strong> 8
<strong>Explanation:</strong>
The possible text messages Alice could have sent are:
&quot;aaadd&quot;, &quot;abdd&quot;, &quot;badd&quot;, &quot;cdd&quot;, &quot;aaae&quot;, &quot;abe&quot;, &quot;bae&quot;, and &quot;ce&quot;.
Since there are 8 possible messages, we return 8.
</pre>

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

<pre>
<strong>Input:</strong> pressedKeys = &quot;222222222222222222222222222222222222&quot;
<strong>Output:</strong> 82876089
<strong>Explanation:</strong>
There are 2082876103 possible text messages Alice could have sent.
Since we need to return the answer modulo 10<sup>9</sup> + 7, we return 2082876103 % (10<sup>9</sup> + 7) = 82876089.
</pre>

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

<ul>
	<li><code>1 &lt;= pressedKeys.length &lt;= 10<sup>5</sup></code></li>
	<li><code>pressedKeys</code> only consists of digits from <code>&#39;2&#39;</code> - <code>&#39;9&#39;</code>.</li>
</ul>