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The following code attempts to add a number to the intervals but contains a subtle bug. Which line causes incorrect behavior when adding a number already covered by an existing interval?

medium🐞 Bug Identification Q14 of Q15

Intervals - Data Stream as Disjoint Intervals

The following code attempts to add a number to the intervals but contains a subtle bug. Which line causes incorrect behavior when adding a number already covered by an existing interval?

AMissing lines checking if val is already covered by existing intervals

BLine calculating i = bisect_left(intervals, [val, val])

CLine checking if intervals is empty and appending [val, val]

DLine popping intervals[i] after merging two intervals

Step-by-Step Solution

Solution:

Step 1: Identify missing coverage check
The code lacks checks to return early if val is already inside intervals[i-1] or intervals[i].
Step 2: Consequence of missing check
Without this, duplicates or incorrect merges occur, corrupting intervals.
Final Answer:
Option A -> Option A
Quick Check:
Missing coverage check causes incorrect behavior [OK]

Quick Trick: Always check if val is already covered before inserting [OK]

Common Mistakes:

MISTAKES

Forgetting coverage check
Incorrect merge boundaries
Popping wrong interval

Trap Explanation:

PITFALL

Candidates often overlook coverage checks, assuming bisect_left alone suffices.

Interviewer Note:

CONTEXT

Tests ability to spot subtle correctness bugs in interval merging code.

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