<p>Given an array of strings <code>words</code>, return <em>the words that can be typed using letters of the alphabet on only one row of American keyboard like the image below</em>.</p>

<p>In the <strong>American keyboard</strong>:</p>

<ul>
	<li>the first row consists of the characters <code>&quot;qwertyuiop&quot;</code>,</li>
	<li>the second row consists of the characters <code>&quot;asdfghjkl&quot;</code>, and</li>
	<li>the third row consists of the characters <code>&quot;zxcvbnm&quot;</code>.</li>
</ul>
<img alt="" src="https://assets.leetcode.com/uploads/2018/10/12/keyboard.png" style="width: 800px; max-width: 600px; height: 267px;" />
<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> words = [&quot;Hello&quot;,&quot;Alaska&quot;,&quot;Dad&quot;,&quot;Peace&quot;]
<strong>Output:</strong> [&quot;Alaska&quot;,&quot;Dad&quot;]
</pre>

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

<pre>
<strong>Input:</strong> words = [&quot;omk&quot;]
<strong>Output:</strong> []
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> words = [&quot;adsdf&quot;,&quot;sfd&quot;]
<strong>Output:</strong> [&quot;adsdf&quot;,&quot;sfd&quot;]
</pre>

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

<ul>
	<li><code>1 &lt;= words.length &lt;= 20</code></li>
	<li><code>1 &lt;= words[i].length &lt;= 100</code></li>
	<li><code>words[i]</code> consists of English letters (both lowercase and uppercase).&nbsp;</li>
</ul>

class Solution {
public:
    vector<string> findWords(vector<string>& words) {
        unordered_set<char> row1 = {'q', 'w', 'e', 'r', 't', 'y', 'u', 'i', 'o', 'p'};
        unordered_set<char> row2 = {'a', 's', 'd', 'f', 'g', 'h', 'j', 'k', 'l'};
        unordered_set<char> row3 = {'z', 'x', 'c', 'v', 'b', 'n', 'm'};
        
        vector<string> result;
        
        auto canBeTypedWithOneRow = [&](const string& word, const unordered_set<char>& row) {
            for (char ch : word) {
                if (row.find(tolower(ch)) == row.end()) {
                    return false;
                }
            }
            return true;
        };
        
        for (const string& word : words) {
            if (canBeTypedWithOneRow(word, row1) || canBeTypedWithOneRow(word, row2) || canBeTypedWithOneRow(word, row3)) {
                result.push_back(word);
            }
        }
        
        return result;
    }
};
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