← Meta Interview Insights

Meta·Software Engineer·Technical Phone Screen·Intermediate

Intermediate
Jun 2026

Summary

Meta SWE coding round, one question on interval merging. Pretty standard stuff but the edge cases are where they actually watch you think.

Questions Asked (1)

Q1

Given a list of intervals, merge all overlapping ones and return the result sorted by start time.

Algorithms & Data Structures
Author's notes

The base case tripped me up more than I expected.

Create a free account to read the full note

AI HintsAI Generated

Suggested Approach

Start by clarifying edge cases and input assumptions, then propose sorting the intervals by start time and merging in a single pass. Walk through the algorithm with a concrete example, analyze time and space complexity, and discuss potential optimizations or alternative approaches.

Pro tip: At Meta, interviewers value clean, efficient code and the ability to handle edge cases gracefully. Before coding, explicitly state your assumptions and confirm them with the interviewer to avoid misunderstandings.

1. Clarify requirements and edge cases

Ask about input format, whether intervals are inclusive, if the list can be empty, and if intervals are already sorted. Confirm expected output format.

2. Outline the approach

Explain that sorting by start time allows merging overlapping intervals in a single pass. Mention that you'll iterate through the sorted list, merging when the current interval overlaps with the last merged one.

3. Walk through an example

Choose a small example (e.g., [[1,3],[2,6],[8,10],[15,18]]) and demonstrate step-by-step how the algorithm merges intervals and produces the output.

4. Analyze complexity and discuss trade-offs

State that sorting takes O(n log n) time and merging takes O(n), so overall O(n log n) time. Space is O(n) for the output (or O(log n) if sorting in-place). Discuss if input is already sorted, we can skip sorting and achieve O(n).

5. Code and test

Write clean code with meaningful variable names, handle edge cases (empty list, single interval), and test with the example and additional cases like non-overlapping intervals.

Key Points to Mention

  • Sorting by start time is crucial for the single-pass merge.
  • Overlap condition: next.start <= current.end (for inclusive intervals).
  • Edge cases: empty input, single interval, intervals with same start time, touching intervals (e.g., [1,2] and [2,3] may or may not be considered overlapping depending on definition).
  • Time complexity: O(n log n) due to sorting; space complexity: O(n) for output.
  • If input is already sorted, we can merge in O(n) time.
  • Alternative approaches: using a stack or in-place merging if modifying input is allowed.

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.