<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 Trie: 
    def __init__(self): 
        self.root = {}
    
    def insert(self, word, k): 
        node = self.root 
        for i, c in enumerate(word): 
            if word[i:] == word[i:][::-1]: node.setdefault("val", []).append(k)
            node = node.setdefault(c, {})
        node.setdefault("val", []).append(k)
        node.setdefault("end", []).append(k)
            
    def search(self, word): 
        ans = []
        node = self.root
        for i, c in enumerate(word): 
            if word[i:] == word[i:][::-1]: ans.extend(node.get("end", []))
            if c not in node: break 
            node = node[c]
        else: ans += node.get("val", [])
        return ans 
    

class Solution:
    def palindromePairs(self, words: List[str]) -> List[List[int]]:
        trie = Trie()
        for i, word in enumerate(words): 
            trie.insert(word, i)
        
        ans = set()
        for i, word in enumerate(words): 
            val = trie.search(word[::-1])
            for ii in val: 
                if ii != i: ans.add((ii, i))
        return ans 
105858