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What is the time complexity of the optimal algorithm that determines if a person can attend all meetings given n intervals, where the algorithm sorts intervals by start time and then checks for overlaps in a single pass?

medium🪤 Complexity Trap Q13 of Q15
Intervals - Meeting Rooms I
What is the time complexity of the optimal algorithm that determines if a person can attend all meetings given n intervals, where the algorithm sorts intervals by start time and then checks for overlaps in a single pass?
AO(n) because we only scan the intervals once after sorting
BO(n^2) because each interval is compared with all others for overlaps
CO(n log n) due to sorting the intervals by start time
DO(log n) because sorting can be done in logarithmic time
Step-by-Step Solution
  1. Step 1: Identify sorting cost

    Sorting n intervals by start time takes O(n log n) time.
  2. Step 2: Identify overlap check cost

    Single pass to check overlaps is O(n), which is dominated by sorting.
  3. Final Answer:

    Option C -> Option C
  4. Quick Check:

    Sorting dominates total time complexity [OK]
Quick Trick: Sorting dominates complexity -> O(n log n) [OK]
Common Mistakes:
MISTAKES
  • Confusing single pass check as O(n log n)
  • Assuming nested loops cause O(n^2) here
Trap Explanation:
PITFALL
  • Candidates often mistake the overlap check as O(n^2) or ignore sorting cost, making O(n) or O(n^2) plausible but incorrect.
Interviewer Note:
CONTEXT
  • Tests understanding of sorting cost and single pass checks in interval problems.
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