<p>Given a string <code>s</code>, consider all <em>duplicated substrings</em>: (contiguous) substrings of s that occur 2 or more times.&nbsp;The occurrences&nbsp;may overlap.</p>

<p>Return <strong>any</strong> duplicated&nbsp;substring that has the longest possible length.&nbsp;If <code>s</code> does not have a duplicated substring, the answer is <code>&quot;&quot;</code>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<pre><strong>Input:</strong> s = "banana"
<strong>Output:</strong> "ana"
</pre><p><strong class="example">Example 2:</strong></p>
<pre><strong>Input:</strong> s = "abcd"
<strong>Output:</strong> ""
</pre>
<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>2 &lt;= s.length &lt;= 3 * 10<sup>4</sup></code></li>
	<li><code>s</code> consists of lowercase English letters.</li>
</ul>

class Solution {
public:
    string longestDupSubstring(string s) {
        string_view longest;
        unordered_set<string_view> st;

        int left = 1, right = s.size()-1;

        while(left <= right){
            int middle = (left + right) / 2;
            bool found = false;
            for(int i=0; i<=s.size()-middle; i++){
                const auto [it, inserted] = st.emplace(s.data()+i, middle);
                if(!inserted){
                    found = true;
                    longest = *it;
                    break;
                }
            }

            if(found)
                left = middle + 1;
            else
                right = middle - 1;
            st.clear();
        }

        return {longest.begin(), longest.end()};
    }
};
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