<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 {
public:
    vector<int> palindrome_suffix_indices;
    unordered_map<char, TrieNode*> children;
    int index;

    TrieNode() : index(-1) {}
};

class Trie {
public:
    TrieNode* root;

    Trie() { 
        root = new TrieNode(); 
    }

    void insert(string word, int index) {
        TrieNode* node = root;
        for (int i = word.size() - 1; i >= 0; --i) {
            if (isPalindrome(word, 0, i)) {
                node->palindrome_suffix_indices.push_back(index);
            }
            if (!node->children.count(word[i])) {
                node->children[word[i]] = new TrieNode();
            }
            node = node->children[word[i]];
        }
        node->index = index;
        node->palindrome_suffix_indices.push_back(index);
    }

    bool isPalindrome(const string& word, int left, int right) {
        while (left < right) {
            if (word[left++] != word[right--]) {
                return false;
            }
        }
        return true;
    }

    void search(const vector<string>& words, int i,
                vector<vector<int>>& result) {
        TrieNode* node = root;
        for (int j = 0; j < words[i].size(); ++j) {
            if (node->index >= 0 && node->index != i &&
                isPalindrome(words[i], j, words[i].size() - 1)) {
                result.push_back({i, node->index});
            }
            if (!node->children.count(words[i][j])) {
                return;
            }
            node = node->children[words[i][j]];
        }
        for (int j : node->palindrome_suffix_indices) {
            if (i != j) {
                result.push_back({i, j});
            }
        }
    }
};

class Solution {
public:
    vector<vector<int>> palindromePairs(vector<string>& words) {
        Trie trie;
        vector<vector<int>> result;

        // Insert all words into the Trie
        for (int i = 0; i < words.size(); ++i) {
            trie.insert(words[i], i);
        }

        // Search for palindrome pairs
        for (int i = 0; i < words.size(); ++i) {
            trie.search(words, i, result);
        }

        return result;
    }
};

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