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Java-based LeetCode algorithm problem solutions, regularly updated
336\. Palindrome Pairs
Hard
Given a list of **unique** words, return all the pairs of the **_distinct_** indices `(i, j)` in the given list, so that the concatenation of the two words `words[i] + words[j]` is a palindrome.
**Example 1:**
**Input:** words = ["abcd","dcba","lls","s","sssll"]
**Output:** [[0,1],[1,0],[3,2],[2,4]]
**Explanation:** The palindromes are ["dcbaabcd","abcddcba","slls","llssssll"]
**Example 2:**
**Input:** words = ["bat","tab","cat"]
**Output:** [[0,1],[1,0]]
**Explanation:** The palindromes are ["battab","tabbat"]
**Example 3:**
**Input:** words = ["a",""]
**Output:** [[0,1],[1,0]]
**Constraints:**
* `1 <= words.length <= 5000`
* `0 <= words[i].length <= 300`
* `words[i]` consists of lower-case English letters.