<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 TrieNode:
    def __init__(self):
        self.children = dict()
        self.end = False
        self.idx = -1
        self.palindromeIdxs = list()

class Solution:
    def __init__(self):
        self.root = TrieNode()
        
    def palindromePairs(self, words: List[str]) -> List[List[int]]:
        res = list()
        
        for i in range(len(words)):
            cur = self.root
            word_rev = words[i][::-1]
            for j in range(len(word_rev)):
                if self.isPalindrome(word_rev[j:]):
                    cur.palindromeIdxs.append(i)
                
                if word_rev[j] not in cur.children:
                    cur.children[word_rev[j]] = TrieNode()
                cur = cur.children[word_rev[j]]
            
            cur.end = True
            cur.idx = i
        
        for i in range(len(words)):
            self.search(words[i], i, res)
            
        return res
    
    def search(self, word, idx, res):   
        cur = self.root
        for i in range(len(word)):
            if cur.end and self.isPalindrome(word[i:]):
                res.append([idx, cur.idx])
                
            if word[i] not in cur.children:
                return
            cur = cur.children[word[i]]        
        
        if cur.end and cur.idx != idx:
            res.append([cur.idx, idx])
        
        for pIdx in cur.palindromeIdxs:
            res.append([idx, pIdx])
                
        return
        
    def isPalindrome(self, s):
        return s == s[::-1]
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