<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]]:
        root = [{}, [], -1]
        for i, w in enumerate(words):
            w = w[::-1]
            node = root
            for j, c in enumerate(w):
                if w[j:] == w[j:][::-1]:
                    node[1].append(i)
                if c not in node[0]:
                    node[0][c] = [{}, [], -1]
                node = node[0][c]
            node[2] = i
        l = []
        for i, w in enumerate(words):
            node = root
            for j, c in enumerate(w):
                if w[j:] == w[j:][::-1] and node[2] != -1:
                    l.append([i, node[2]])
                if c not in node[0]:
                    break
                node = node[0][c]
            else:
                if node[2] != -1 and node[2] != i:
                    l.append([i, node[2]])
                for j in node[1]:
                    l.append([i, j])
        return l

        # l = []
        # m = {w[::-1]: i for i, w in enumerate(words)}
        # for i, w in enumerate(words):
        #     if w in m and i != m[w]:
        #         l.append([i, m[w]])
        #     for j in range(len(w)):
        #         s = w[j:]
        #         rs = w[:j]
        #         if s == s[::-1] and rs in m and i != m[rs]:
        #             l.append([i, m[rs]])
        #         p = w[:j + 1]
        #         rp = w[j + 1:]
        #         if p == p[::-1] and rp in m and i != m[rp]:
        #             l.append([m[rp], i])
        # return l
        
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