<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 {
public:
    vector<vector<int>> palindromePairs(vector<string>& words) {
        vector<tuple<string, int, bool>> v;
        for (size_t i = 0; i < words.size(); i++) {
            v.emplace_back(words[i], i, false);
        }
        for (size_t i = 0; i < words.size(); i++) {
            string s = words[i];
            reverse(s.begin(), s.end());
            v.emplace_back(s, i, true);
        }
        sort(v.begin(), v.end(), [](auto& a, auto& b) {
            return get<0>(a) < get<0>(b);
        });
        vector<vector<int>> ans;
        for (size_t i = 0; i < v.size(); i++) {
            auto& [s1, idx1, is_reserved1] = v[i];
            for (size_t j = i + 1; j < v.size(); j++) {
                auto& [s2, idx2, is_reserved2] = v[j];
                if (s2.rfind(s1, 0) != 0) break;
                if (is_reserved1 == is_reserved2) continue;
                if (idx1 == idx2) continue;
                if (!is_palindrome(s2, s1.size(), s2.size() - 1)) continue;
                if (is_reserved2) ans.push_back({idx1, idx2});
                else ans.push_back({idx2, idx1});
            }
        }
        return ans;
    }

private:
    bool is_palindrome (string& s, int i, int j) {
        while (i < j) {
            if (s[i] != s[j]) return false;
            i++, j--;
        }
        return true;
    }
};
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