Started with the brute force two-pointer approach and the interviewer just kind of waited.
Start by clarifying the problem: whether pairs are ordered, if duplicates are allowed, and if the array is sorted. Then propose an efficient solution using a hash set to track seen elements, checking for both x + k and x - k to handle absolute difference. Discuss time and space complexity, and consider edge cases like k = 0 and negative numbers.
Pro tip: Mention that if the array is sorted, a two-pointer approach can find pairs in O(n) time with O(1) extra space, but sorting takes O(n log n). This shows you understand trade-offs and can adapt to constraints.
Ask if the array is sorted, if pairs are ordered, if duplicates should be counted, and if k can be zero or negative. This ensures you solve the correct problem.
Decide between hash set (O(n) time, O(n) space) and sorting + two pointers (O(n log n) time, O(1) space). Explain your choice based on constraints.
For hash set: iterate through array, for each element check if element + k or element - k exists in set, then add element to set. For two pointers: sort array, use left and right pointers to find pairs with difference k.
State time and space complexity. Discuss edge cases: empty array, k = 0 (need to handle duplicates), negative numbers, and large k.
Walk through a small example to verify correctness, such as array [1, 5, 3, 4, 2] and k = 2, showing pairs (1,3), (3,5), (2,4).
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.