<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.trie = {}
                self.palindromes = []
                self.index = -1
            
            def __repr__(self):
                z = f'{self.palindromes}'
                z += f', index = {self.index}'
                z += ', trie =' + repr(self.trie)
                return z

            def add_word(self, word, k):
                curr = self
                for i in range(len(word)):
                    ch = word[i]
                    if ch not in curr.trie:
                        curr.trie[ch] = TrieNode()
                    curr = curr.trie[ch]
                    if i<len(word)-1 and word[i+1:] == word[i+1:][::-1]:
                        curr.palindromes.append(k)
                curr.index = k
        
            def match_prefix(self, word, k):
                curr = self
                ans = []
                for i in reversed(range(len(word))):
                    ch = word[i]
                    # print(ch)
                    if ch not in curr.trie:
                        return ans 
                    curr = curr.trie[ch]
                    if curr.index != -1 and curr.index != k:
                        if word[:i] == word[:i][::-1]:
                            ans.append([curr.index, k])
                    # print(ans)

                for j in curr.palindromes:
                    if j != k:
                        ans.append([j, k])
                        print(ans)
                return ans


        tobj = TrieNode()
        for k in range(len(words)):
            tobj.add_word(words[k], k)

        # print(repr(tobj.trie))
        rs = []
        for k in range(len(words)):
            rs += tobj.match_prefix(words[k], k)
            # print('&', words[k], k, rs)
            # print(words[k], k)

        if tobj.index != -1:
            j = tobj.index
            for i in range(len(words)):
                if i == j:
                    continue
                if words[i] == words[i][::-1]:
                    rs.append([i, j])
                    rs.append([j, i])

        return rs



        
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