<p>Given a string array <code>words</code>, return <em>the maximum value of</em> <code>length(word[i]) * length(word[j])</code> <em>where the two words do not share common letters</em>. If no such two words exist, return <code>0</code>.</p>

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

<pre>
<strong>Input:</strong> words = [&quot;abcw&quot;,&quot;baz&quot;,&quot;foo&quot;,&quot;bar&quot;,&quot;xtfn&quot;,&quot;abcdef&quot;]
<strong>Output:</strong> 16
<strong>Explanation:</strong> The two words can be &quot;abcw&quot;, &quot;xtfn&quot;.
</pre>

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

<pre>
<strong>Input:</strong> words = [&quot;a&quot;,&quot;ab&quot;,&quot;abc&quot;,&quot;d&quot;,&quot;cd&quot;,&quot;bcd&quot;,&quot;abcd&quot;]
<strong>Output:</strong> 4
<strong>Explanation:</strong> The two words can be &quot;ab&quot;, &quot;cd&quot;.
</pre>

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

<pre>
<strong>Input:</strong> words = [&quot;a&quot;,&quot;aa&quot;,&quot;aaa&quot;,&quot;aaaa&quot;]
<strong>Output:</strong> 0
<strong>Explanation:</strong> No such pair of words.
</pre>

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

<ul>
	<li><code>2 &lt;= words.length &lt;= 1000</code></li>
	<li><code>1 &lt;= words[i].length &lt;= 1000</code></li>
	<li><code>words[i]</code> consists only of lowercase English letters.</li>
</ul>

class Solution {
public:
    string foo(const std::string s)
    {
        std::string r;
        char m[256] = { 0 };
        for (const auto c : s)
        {
            const auto u = (unsigned char)c;
            if (m[u] == 0)
            {
                m[u] = 1;
                r.push_back(c);
            }
        }
        return r;
    }
    int maxProduct(vector<string>& words) {
        vector<string> word = words;
        int maxi = 0;
        for (int i = 0; i < words.size(); ++i)
        {
            word[i] = foo(words[i]);
        }
        for (int i = 0; i < words.size(); ++i)
        {
            for (int j = 0; j < words.size(); ++j)
            {
                if (words[i] != words[j])
                {
                    if (word[i].size() + word[j].size() == foo(word[i] + word[j]).size())
                    {
                        maxi = max(maxi, (int)(words[i].size() * words[j].size()));
                    }
                }
            }
        }
        return maxi;
    }
};
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