Start by clarifying the problem and constraints, then propose a hash map-based solution that stores reversed words and checks for palindromic splits, handling edge cases like empty strings and duplicates. Walk through the algorithm step-by-step, analyze time and space complexity, and discuss test cases including large inputs.
Pro tip: Emphasize that the total character count is 200,000, so an O(total characters) solution is feasible; mention that using a trie can optimize further but a hash map is simpler and sufficient. Also, proactively discuss how to avoid duplicate pairs by enforcing i < j or using a set.
Confirm understanding of the problem: distinct lowercase strings, find all index pairs (i, j) with i != j such that words[i] + words[j] is a palindrome. Note constraints: up to 100,000 words, total characters 200,000, need better than O(n^2 * L).
Use a hash map to store each word's index for O(1) lookups. For each word, consider all possible splits into prefix and suffix, check if one part is a palindrome and the other's reverse exists in the map.
Address empty strings: if a word is empty, it can pair with any palindrome word. Single characters are palindromes. Ensure no duplicate pairs by only adding when i != j and using a set or checking indices.
Time: O(N * L^2) worst-case if checking each split naively, but with precomputed palindrome checks or efficient methods, it can be O(total characters * average word length) or O(N * L) with optimizations. Space: O(N * L) for the hash map.
Include: empty array, single word, words with empty string, words like 'a', 'ab', 'ba', 'abc', 'cba', and large random inputs to verify performance. Check for duplicate pairs and correct palindrome formation.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.