336 - Palindrome Pairs\.

Hard

You are given a 0-indexed array of unique strings words.

A palindrome pair is a pair of integers (i, j) such that:

• 0 <= i, j < word.length,

• i != j, and

• words[i] + words[j] (the concatenation of the two strings) is a palindrome.

Return an array of all the palindrome pairs of words.

Example 1:

Input: words = "abcd","dcba","lls","s","sssll"

Output: [0,1,1,0,3,2,2,4]

Explanation: The palindromes are "abcddcba","dcbaabcd","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]

Explanation: The palindromes are "a","a"

Constraints:

• 1 <= words.length <= 5000

• 0 <= words[i].length <= 300

• words[i] consists of lowercase English letters.