<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.map = {}
        self.index = -1
        self.palindrome_idx_list = []
        self.end = False
    
    
class Solution:
    
    
    def __init__(self):
        self.node = TrieNode()
    
    def insert(self, word, idx):
        current = self.node
        for index in range(len(word)):
            if self.is_palindrome(word[index:]):
                current.palindrome_idx_list.append(idx)
            ch = word[index]
            if ch not in current.map.keys():
                current.map[ch] = TrieNode()
            current = current.map[ch]
        current.index = idx
        current.end = True
    
    def search(self, word, idx, result):
        current = self.node
        for index in range(len(word)):
            if current.end and self.is_palindrome(word[index:]):
                result.append((idx, current.index))
            if word[index] not in current.map.keys():
                return
            current = current.map[word[index]]
        if current.end and idx != current.index:
            result.append((idx, current.index))
        for p in current.palindrome_idx_list:
            result.append((idx, p))
        return 
    
    def palindromePairs(self, words: List[str]) -> List[List[int]]:
        
        for index in range(len(words)):
            self.insert(words[index][::-1], index)
        
        result = []
        
        for index in range(len(words)):
            self.search(words[index], index, result)
        
        return result
    
    def is_palindrome(self, word):
        start, end = 0, len(word)-1
        while start < end:
            if word[start] != word[end]:
                return False
            start += 1
            end -= 1
        return True
            
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