Vowel Spellchecker
<p>Given a <code>wordlist</code>, we want to implement a spellchecker that converts a query word into a correct word.</p>

<p>For a given <code>query</code> word, the spell checker handles two categories of spelling mistakes:</p>

<ul>
	<li>Capitalization: If the query matches a word in the wordlist (<strong>case-insensitive</strong>), then the query word is returned with the same case as the case in the wordlist.

    <ul>
    	<li>Example: <code>wordlist = [&quot;yellow&quot;]</code>, <code>query = &quot;YellOw&quot;</code>: <code>correct = &quot;yellow&quot;</code></li>
    	<li>Example: <code>wordlist = [&quot;Yellow&quot;]</code>, <code>query = &quot;yellow&quot;</code>: <code>correct = &quot;Yellow&quot;</code></li>
    	<li>Example: <code>wordlist = [&quot;yellow&quot;]</code>, <code>query = &quot;yellow&quot;</code>: <code>correct = &quot;yellow&quot;</code></li>
    </ul>
    </li>
    <li>Vowel Errors: If after replacing the vowels <code>(&#39;a&#39;, &#39;e&#39;, &#39;i&#39;, &#39;o&#39;, &#39;u&#39;)</code> of the query word with any vowel individually, it matches a word in the wordlist (<strong>case-insensitive</strong>), then the query word is returned with the same case as the match in the wordlist.
    <ul>
    	<li>Example: <code>wordlist = [&quot;YellOw&quot;]</code>, <code>query = &quot;yollow&quot;</code>: <code>correct = &quot;YellOw&quot;</code></li>
    	<li>Example: <code>wordlist = [&quot;YellOw&quot;]</code>, <code>query = &quot;yeellow&quot;</code>: <code>correct = &quot;&quot;</code> (no match)</li>
    	<li>Example: <code>wordlist = [&quot;YellOw&quot;]</code>, <code>query = &quot;yllw&quot;</code>: <code>correct = &quot;&quot;</code> (no match)</li>
    </ul>
    </li>

</ul>

<p>In addition, the spell checker operates under the following precedence rules:</p>

<ul>
	<li>When the query exactly matches a word in the wordlist (<strong>case-sensitive</strong>), you should return the same word back.</li>
	<li>When the query matches a word up to capitlization, you should return the first such match in the wordlist.</li>
	<li>When the query matches a word up to vowel errors, you should return the first such match in the wordlist.</li>
	<li>If the query has no matches in the wordlist, you should return the empty string.</li>
</ul>

<p>Given some <code>queries</code>, return a list of words <code>answer</code>, where <code>answer[i]</code> is the correct word for <code>query = queries[i]</code>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<pre><strong>Input:</strong> wordlist = ["KiTe","kite","hare","Hare"], queries = ["kite","Kite","KiTe","Hare","HARE","Hear","hear","keti","keet","keto"]
<strong>Output:</strong> ["kite","KiTe","KiTe","Hare","hare","","","KiTe","","KiTe"]
</pre><p><strong class="example">Example 2:</strong></p>
<pre><strong>Input:</strong> wordlist = ["yellow"], queries = ["YellOw"]
<strong>Output:</strong> ["yellow"]
</pre>
<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= wordlist.length, queries.length &lt;= 5000</code></li>
	<li><code>1 &lt;= wordlist[i].length, queries[i].length &lt;= 7</code></li>
	<li><code>wordlist[i]</code> and <code>queries[i]</code> consist only of only English letters.</li>
</ul>
Array; Hash Table; String
class Solution {
public:
    vector<string> spellchecker(vector<string>& wordlist, vector<string>& queries) {
        unordered_set<string> s(wordlist.begin(), wordlist.end());
        unordered_map<string, string> low;
        unordered_map<string, string> pat;
        auto f = [](string& w) {
            string res;
            for (char& c : w) {
                if (c == 'a' || c == 'e' || c == 'i' || c == 'o' || c == 'u') {
                    res += '*';
                } else {
                    res += c;
                }
            }
            return res;
        };
        for (auto& w : wordlist) {
            string t = w;
            transform(t.begin(), t.end(), t.begin(), ::tolower);
            if (!low.count(t)) {
                low[t] = w;
            }
            t = f(t);
            if (!pat.count(t)) {
                pat[t] = w;
            }
        }
        vector<string> ans;
        for (auto& q : queries) {
            if (s.count(q)) {
                ans.emplace_back(q);
                continue;
            }
            transform(q.begin(), q.end(), q.begin(), ::tolower);
            if (low.count(q)) {
                ans.emplace_back(low[q]);
                continue;
            }
            q = f(q);
            if (pat.count(q)) {
                ans.emplace_back(pat[q]);
                continue;
            }
            ans.emplace_back("");
        }
        return ans;
    }
};