<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:
    vector<string> findRepeatedDnaSequences(string s) {
        vector<string> res;
        int n=s.length();

        int label[n];
        for(int i=0;i<n;i++){
            if(s[i]=='A')   label[i]=0; //00
            else if(s[i]=='C')  label[i]=1; //01
            else if(s[i]=='G')  label[i]=2; //10
            else    label[i]=3; //11
        }

        long long int hash_val=0;
        unordered_map<int,int>mp;
        for(int i=0;i<n-9;i++){
            if(i==0){
                for(int i=0;i<10;i++){
                    hash_val= (hash_val<<2) + label[i]; //converting to decimal number  
                }
                mp[hash_val]++;
            }
            else{
                // Finding new hash value 
                hash_val = (hash_val<<2) - (label[i - 1]<<20) + label[i + 9]; 
                mp[hash_val]++;
                if(mp[hash_val]==2){
                    res.push_back(s.substr(i,10));
                }
            }
        }
        return res;
    }
};
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