<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:
    bool isSubPalindrome(string& s, int l, int r) {
        while (l < r) {
            if (s[l] != s[r])
                return false;
            l++;
            r--;
        }
        return true;
    }

    vector<string> getPrefixes(string& s) {
        vector<string> res;
        int n = s.size();
        for (int i = 0; i < n; i++) {
            if (isSubPalindrome(s, i, n-1)) {
                res.push_back(s.substr(0, i));
            }
        }
        return res;
    }

    vector<string> getSuffixes(string& s) {
        vector<string> res;
        int n = s.size();
        for (int i = 0; i < n; i++) {
            if (isSubPalindrome(s, 0, i)) {
                int len = n - (i+1);
                res.push_back(s.substr(i+1, len));
            }
        }
        return res;
    }
    
    vector<vector<int>> palindromePairs(vector<string>& words) {
        unordered_map<string, int> mp;
        for (int i = 0; i < words.size(); i++) {
            mp[words[i]] = i;
        }

        vector<vector<int>> res;
        for (auto [word, i]: mp) {
            string rev = word;
            string s = word;
            reverse(rev.begin(), rev.end());
            if (mp.contains(rev) && mp[rev] != i) {
                res.push_back({i, mp[rev]});
            }

            vector<string> suff = getSuffixes(s);
            for (auto suf: suff) {
                reverse(suf.begin(), suf.end());
                if (mp.contains(suf) && mp[suf] != i) {
                    res.push_back({mp[suf], i});
                }
            }
            vector<string> pre = getPrefixes(s);
            for (auto p: pre) {
                reverse(p.begin(), p.end());
                if (mp.contains(p) && mp[p] != i) {
                    res.push_back({i, mp[p]});
                }
            }
        }

        return res;
    }
};
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