private void createList(int i1, int i2, List<List<Integer>> result) {
        if (i1 == i2) {
            return;
        }
        List<Integer> r = new ArrayList<>();
        r.add(i1);
        r.add(i2);
        result.add(r);
    }
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.

Solution -
First keep mapping of word and its index.
Then iterate through every word and split it into every possible 2 substring. Then if first substring is palindrome
and reverse of second substring is in map means you can form a palindrome by combing this word with the word
in the map.

Time complexity is O(n*k*k)

Reference
https://leetcode.com/problems/palindrome-pairs/
src/com/interview/string/PalindromePair.java