The core merge logic clicked pretty fast for me, two pointers advancing through both lists, pick the smaller start, extend the end greedily.
Start by clarifying edge cases and assumptions, then outline the two-pointer merge algorithm, emphasizing how to handle touching boundaries and invalid intervals. Conclude with complexity analysis and a brief walkthrough of the algorithm.
Pro tip: Explicitly state your assumptions about interval validity and boundary touching, and ask the interviewer if they want you to handle invalid intervals by skipping or throwing an error. This shows attention to detail and proactive communication.
Ask about handling of empty inputs, invalid intervals (start > end), and whether touching intervals like [1,3] and [3,5] should be merged. Confirm if the output should be sorted and non-overlapping.
Explain that you'll use two pointers, one for each list, to iterate through intervals in sorted order. At each step, pick the interval with the smaller start, and merge if it overlaps or touches the last interval in the result.
Describe how to check for overlap: if the current interval's start <= last merged interval's end, merge by updating the end to max of both ends. For touching boundaries, treat as overlapping if start == end.
Decide on a strategy: either skip invalid intervals or throw an error. Mention that you'll assume inputs are valid unless specified otherwise, but you can add a check.
State that time complexity is O(m+n) and space is O(m+n) for the output. Walk through a small example, including edge cases, to demonstrate correctness.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.