<p>You are given an array of strings <code>words</code>. Each element of <code>words</code> consists of <strong>two</strong> lowercase English letters.</p>

<p>Create the <strong>longest possible palindrome</strong> by selecting some elements from <code>words</code> and concatenating them in <strong>any order</strong>. Each element can be selected <strong>at most once</strong>.</p>

<p>Return <em>the <strong>length</strong> of the longest palindrome that you can create</em>. If it is impossible to create any palindrome, return <code>0</code>.</p>

<p>A <strong>palindrome</strong> is a string that reads the same forward and backward.</p>

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

<pre>
<strong>Input:</strong> words = [&quot;lc&quot;,&quot;cl&quot;,&quot;gg&quot;]
<strong>Output:</strong> 6
<strong>Explanation:</strong> One longest palindrome is &quot;lc&quot; + &quot;gg&quot; + &quot;cl&quot; = &quot;lcggcl&quot;, of length 6.
Note that &quot;clgglc&quot; is another longest palindrome that can be created.
</pre>

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

<pre>
<strong>Input:</strong> words = [&quot;ab&quot;,&quot;ty&quot;,&quot;yt&quot;,&quot;lc&quot;,&quot;cl&quot;,&quot;ab&quot;]
<strong>Output:</strong> 8
<strong>Explanation:</strong> One longest palindrome is &quot;ty&quot; + &quot;lc&quot; + &quot;cl&quot; + &quot;yt&quot; = &quot;tylcclyt&quot;, of length 8.
Note that &quot;lcyttycl&quot; is another longest palindrome that can be created.
</pre>

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

<pre>
<strong>Input:</strong> words = [&quot;cc&quot;,&quot;ll&quot;,&quot;xx&quot;]
<strong>Output:</strong> 2
<strong>Explanation:</strong> One longest palindrome is &quot;cc&quot;, of length 2.
Note that &quot;ll&quot; is another longest palindrome that can be created, and so is &quot;xx&quot;.
</pre>

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

<ul>
	<li><code>1 &lt;= words.length &lt;= 10<sup>5</sup></code></li>
	<li><code>words[i].length == 2</code></li>
	<li><code>words[i]</code> consists of lowercase English letters.</li>
</ul>

class Solution {
public:
    Solution() {
        ios_base::sync_with_stdio(0);
    }
    int longestPalindrome(vector<string>& words) {
        unordered_map<string,int> wordsfreq;
        // ab, ba, ab, ba -> ababbaba 
        // ab, ba, ab, ba, ab ba-> abababbababa
        int ans = 0;
        for(int i=0; i<words.size(); i++)
            wordsfreq[words[i]]++;
        
        bool singleSameStr = false;
        for(auto it : wordsfreq){
            if(it.first[0]==it.first[1]) {
                if(it.second==1) singleSameStr = true;
                else {
                    if(it.second%2==0) ans+=(2*it.second);
                    else {
                        ans+=(2*(it.second-1));
                        singleSameStr = true;
                    }
                }
                continue;
            }
            string reverse ;
            reverse.push_back(it.first[1]);
            reverse.push_back(it.first[0]);

            if(wordsfreq.find(reverse)!=wordsfreq.end() && wordsfreq[reverse]!=-1 ){
                ans+=(4*min(wordsfreq[reverse],wordsfreq[it.first]));
                wordsfreq[reverse]=-1;
                wordsfreq[it.first]=-1;
            }
        }
        // cout<<maxSameCharStr<<endl;
        if(singleSameStr)
        ans+=2;
        return ans;
    }
};
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