<p>You are given a <strong>0-indexed</strong> array of <strong>unique</strong> strings <code>words</code>.</p>

<p>A <strong>palindrome pair</strong> is a pair of integers <code>(i, j)</code> such that:</p>

<ul>
	<li><code>0 &lt;= i, j &lt; words.length</code>,</li>
	<li><code>i != j</code>, and</li>
	<li><code>words[i] + words[j]</code> (the concatenation of the two strings) is a <span data-keyword="palindrome-string">palindrome</span>.</li>
</ul>

<p>Return <em>an array of all the <strong>palindrome pairs</strong> of </em><code>words</code>.</p>

<p>You must write an algorithm with&nbsp;<code>O(sum of words[i].length)</code>&nbsp;runtime complexity.</p>

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

<pre>
<strong>Input:</strong> words = [&quot;abcd&quot;,&quot;dcba&quot;,&quot;lls&quot;,&quot;s&quot;,&quot;sssll&quot;]
<strong>Output:</strong> [[0,1],[1,0],[3,2],[2,4]]
<strong>Explanation:</strong> The palindromes are [&quot;abcddcba&quot;,&quot;dcbaabcd&quot;,&quot;slls&quot;,&quot;llssssll&quot;]
</pre>

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

<pre>
<strong>Input:</strong> words = [&quot;bat&quot;,&quot;tab&quot;,&quot;cat&quot;]
<strong>Output:</strong> [[0,1],[1,0]]
<strong>Explanation:</strong> The palindromes are [&quot;battab&quot;,&quot;tabbat&quot;]
</pre>

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

<pre>
<strong>Input:</strong> words = [&quot;a&quot;,&quot;&quot;]
<strong>Output:</strong> [[0,1],[1,0]]
<strong>Explanation:</strong> The palindromes are [&quot;a&quot;,&quot;a&quot;]
</pre>

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

<ul>
	<li><code>1 &lt;= words.length &lt;= 5000</code></li>
	<li><code>0 &lt;= words[i].length &lt;= 300</code></li>
	<li><code>words[i]</code> consists of lowercase English letters.</li>
</ul>

class Solution {
public:
unordered_map<string,bool>check;
bool palin(string &s)
{
    if(check.find(s)!=check.end())
    {
        return check[s];
    }
    int n=s.size();
    for(int i=0;i<s.size()/2;i++)
    {
        if(s[i]!=s[n-i-1])
        return check[s]=false;
    }
    return check[s]=true;
}
    vector<vector<int>> palindromePairs(vector<string>& s) {
        unordered_map<string,int>mp;
        vector<vector<int>>ans;
        for(int i = 0 ; i < s.size(); i++)
        {
            string str = s[i];
            reverse(str.begin(), str.end());
            mp[str] = i;
        }
        int n= s.size();
        if(mp.find("")!=mp.end())
        {
            for(int i=0;i<n;i++)
            {
                if(s[i]=="""") continue;
                if(palin(s[i]))
                ans.push_back({i,mp[""]});
            }
        }
        for(int i=0;i<n;i++)
        {
            string faka="";
            string ase=s[i];
            for(int j=0;j<s[i].size();j++)
            {
                faka.push_back(s[i][j]);
                ase.erase(ase.begin() + 0);
                if(mp.find(faka) != mp.end() and palin(ase) and mp[faka] != i)
                    ans.push_back({i, mp[faka]});
                
                if(mp.find(ase) != mp.end() and palin(faka) and mp[ase] != i)
                    ans.push_back({mp[ase], i});
            }
        }
        return ans;
        
    }

};
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