<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:
    def palindromePairs(self, words: List[str]) -> List[List[int]]:

        class TrieNode:
            def __init__(self):
                self.children = defaultdict(TrieNode)
                self.palin = []
                self.ending = -1

        root = TrieNode()
        index = 0
        for word in words:            
            current = root
            for i, c in enumerate(word):                
                if word[i:] == word[i:][::-1]:                    
                    current.palin.append(index)
                current = current.children[c]
            current.ending = index
            index += 1

        result = []
        index = 0
        for word in words:
            rev = word[::-1]
            brk = False
            current = root

            for i, c in enumerate(rev):
                if current.ending != -1:
                    if rev[i:] == rev[i:][::-1]:
                        result.append([current.ending, index])

                if c not in current.children:
                    brk = True
                    break
                
                current = current.children[c]
            # print(word, current.children.keys(), brk, result, current.ending, index)
            if not brk:
                if current.ending != -1 and index != current.ending:
                    result.append([current.ending, index])
            
                if len(current.palin) > 0:
                    for i in current.palin:
                        result.append([i, index])

            index+=1
        return result
    
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