336. Palindrome Pairs (Hard)

Given a list of unique words, find all pairs of distinct indices(i, j)in the given list, so that the concatenation of the two words, i.e.words[i] + words[j]is a palindrome.

Example 1:
Givenwords=["bat", "tab", "cat"]
Return[[0, 1], [1, 0]]
The palindromes are["battab", "tabbat"]

Example 2:
Givenwords=["abcd", "dcba", "lls", "s", "sssll"]
Return[[0, 1], [1, 0], [3, 2], [2, 4]]
The palindromes are["dcbaabcd", "abcddcba", "slls", "llssssll"]