<p>The <strong>DNA sequence</strong> is composed of a series of nucleotides abbreviated as <code>&#39;A&#39;</code>, <code>&#39;C&#39;</code>, <code>&#39;G&#39;</code>, and <code>&#39;T&#39;</code>.</p>

<ul>
	<li>For example, <code>&quot;ACGAATTCCG&quot;</code> is a <strong>DNA sequence</strong>.</li>
</ul>

<p>When studying <strong>DNA</strong>, it is useful to identify repeated sequences within the DNA.</p>

<p>Given a string <code>s</code> that represents a <strong>DNA sequence</strong>, return all the <strong><code>10</code>-letter-long</strong> sequences (substrings) that occur more than once in a DNA molecule. You may return the answer in <strong>any order</strong>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<pre><strong>Input:</strong> s = "AAAAACCCCCAAAAACCCCCCAAAAAGGGTTT"
<strong>Output:</strong> ["AAAAACCCCC","CCCCCAAAAA"]
</pre><p><strong class="example">Example 2:</strong></p>
<pre><strong>Input:</strong> s = "AAAAAAAAAAAAA"
<strong>Output:</strong> ["AAAAAAAAAA"]
</pre>
<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= s.length &lt;= 10<sup>5</sup></code></li>
	<li><code>s[i]</code> is either <code>&#39;A&#39;</code>, <code>&#39;C&#39;</code>, <code>&#39;G&#39;</code>, or <code>&#39;T&#39;</code>.</li>
</ul>

class Solution {
public:
    int nucToInt (char c) {
        return c == 'G' ? 2 : c == 'T' ? 3 : c != 'A';
    }
    string intToDNA(int intDNA) {
        string res = "";
        int currNuc;
        while (res.size() < 10) {
            currNuc = intDNA % 4;
            res += currNuc == 3 ? 'T' : currNuc == 2 ? 'G' : currNuc ? 'C' : 'A';
            intDNA >>= 2;
        }
        return res;
    }
    vector<string> findRepeatedDnaSequences(string s) {
        int len = s.size();
        if (len < 10) return {};
        uint32_t intDNA = 0, freq[1048575];
        for (int i = 0; i < 1048575; i++) freq[i] = 0;
        vector<string> res;
        for (int i = 0; i < 10; i++) {
            intDNA >>= 2;
            intDNA += nucToInt(s[i]) << 18;
        }
        freq[intDNA]++;
        for (int i = 10; i < len; i++) {
            intDNA >>= 2;
            intDNA += nucToInt(s[i]) << 18;
            freq[intDNA]++;
            if (freq[intDNA] == 2) {
                res.push_back(intToDNA(intDNA));
            }
        }
        return res;
    }
};
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