leetcode-problemset/leetcode/problem/encrypt-and-decrypt-strings.html

<p>You are given a character array <code>keys</code> containing <strong>unique</strong> characters and a string array <code>values</code> containing strings of length 2. You are also given another string array <code>dictionary</code> that contains all permitted original strings after decryption. You should implement a data structure that can encrypt or decrypt a <strong>0-indexed</strong> string.</p>

<p>A string is <strong>encrypted</strong> with the following process:</p>

<ol>
	<li>For each character <code>c</code> in the string, we find the index <code>i</code> satisfying <code>keys[i] == c</code> in <code>keys</code>.</li>
	<li>Replace <code>c</code> with <code>values[i]</code> in the string.</li>
</ol>

<p>Note that in case a character of the string is <strong>not present</strong> in <code>keys</code>, the encryption process cannot be carried out, and an empty string <code>&quot;&quot;</code> is returned.</p>

<p>A string is <strong>decrypted</strong> with the following process:</p>

<ol>
	<li>For each substring <code>s</code> of length 2 occurring at an even index in the string, we find an <code>i</code> such that <code>values[i] == s</code>. If there are multiple valid <code>i</code>, we choose <strong>any</strong> one of them. This means a string could have multiple possible strings it can decrypt to.</li>
	<li>Replace <code>s</code> with <code>keys[i]</code> in the string.</li>
</ol>

<p>Implement the <code>Encrypter</code> class:</p>

<ul>
	<li><code>Encrypter(char[] keys, String[] values, String[] dictionary)</code> Initializes the <code>Encrypter</code> class with <code>keys, values</code>, and <code>dictionary</code>.</li>
	<li><code>String encrypt(String word1)</code> Encrypts <code>word1</code> with the encryption process described above and returns the encrypted string.</li>
	<li><code>int decrypt(String word2)</code> Returns the number of possible strings <code>word2</code> could decrypt to that also appear in <code>dictionary</code>.</li>
</ul>

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

<pre>
<strong>Input</strong>
[&quot;Encrypter&quot;, &quot;encrypt&quot;, &quot;decrypt&quot;]
[[[&#39;a&#39;, &#39;b&#39;, &#39;c&#39;, &#39;d&#39;], [&quot;ei&quot;, &quot;zf&quot;, &quot;ei&quot;, &quot;am&quot;], [&quot;abcd&quot;, &quot;acbd&quot;, &quot;adbc&quot;, &quot;badc&quot;, &quot;dacb&quot;, &quot;cadb&quot;, &quot;cbda&quot;, &quot;abad&quot;]], [&quot;abcd&quot;], [&quot;eizfeiam&quot;]]
<strong>Output</strong>
[null, &quot;eizfeiam&quot;, 2]

<strong>Explanation</strong>
Encrypter encrypter = new Encrypter([[&#39;a&#39;, &#39;b&#39;, &#39;c&#39;, &#39;d&#39;], [&quot;ei&quot;, &quot;zf&quot;, &quot;ei&quot;, &quot;am&quot;], [&quot;abcd&quot;, &quot;acbd&quot;, &quot;adbc&quot;, &quot;badc&quot;, &quot;dacb&quot;, &quot;cadb&quot;, &quot;cbda&quot;, &quot;abad&quot;]);
encrypter.encrypt(&quot;abcd&quot;); // return &quot;eizfeiam&quot;. 
&nbsp;                          // &#39;a&#39; maps to &quot;ei&quot;, &#39;b&#39; maps to &quot;zf&quot;, &#39;c&#39; maps to &quot;ei&quot;, and &#39;d&#39; maps to &quot;am&quot;.
encrypter.decrypt(&quot;eizfeiam&quot;); // return 2. 
                              // &quot;ei&quot; can map to &#39;a&#39; or &#39;c&#39;, &quot;zf&quot; maps to &#39;b&#39;, and &quot;am&quot; maps to &#39;d&#39;. 
                              // Thus, the possible strings after decryption are &quot;abad&quot;, &quot;cbad&quot;, &quot;abcd&quot;, and &quot;cbcd&quot;. 
                              // 2 of those strings, &quot;abad&quot; and &quot;abcd&quot;, appear in dictionary, so the answer is 2.
</pre>

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

<ul>
	<li><code>1 &lt;= keys.length == values.length &lt;= 26</code></li>
	<li><code>values[i].length == 2</code></li>
	<li><code>1 &lt;= dictionary.length &lt;= 100</code></li>
	<li><code>1 &lt;= dictionary[i].length &lt;= 100</code></li>
	<li>All <code>keys[i]</code> and <code>dictionary[i]</code> are <strong>unique</strong>.</li>
	<li><code>1 &lt;= word1.length &lt;= 2000</code></li>
	<li><code>1 &lt;= word2.length &lt;= 200</code></li>
	<li>All <code>word1[i]</code> appear in <code>keys</code>.</li>
	<li><code>word2.length</code> is even.</li>
	<li><code>keys</code>, <code>values[i]</code>, <code>dictionary[i]</code>, <code>word1</code>, and <code>word2</code> only contain lowercase English letters.</li>
	<li>At most <code>200</code> calls will be made to <code>encrypt</code> and <code>decrypt</code> <strong>in total</strong>.</li>
</ul>