336. Palindrome Pairs

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 < words.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. You must write an algorithm with O(sum of words[i].length) runtime complexity. Example 1: Input: word