Intervals - Count of Intervals Containing Each Point
Using the line sweep algorithm, what is the output for intervals [[3,3]] and points [3,4]?
Using the line sweep algorithm, what is the output for intervals [[3,3]] and points [3,4]?
medium🧾 Code Trace Q4 of Q15
Step-by-Step Solution
Solution:
Step 1: Sort events
Events: (3,+1), (3,0), (3+1=4,-1), (4,0). Sorted by coordinate and type: (3,+1), (3,0), (4,0), (4,-1).Step 2: Process events and count active intervals
At coordinate 3: active increments to 1, point at 3 sees active=1. At coordinate 4: point at 4 sees active=1 before decrementing active to 0.Final Answer:
Option D -> Option DQuick Check:
Point at interval end+1 still counts active intervals before decrement [OK]
Quick Trick: Events at same coordinate: start (+1) before point (0) before end (-1) [OK]
Common Mistakes:
MISTAKES- Assuming point at end+1 is outside interval coverage
- Misordering events causing wrong active count
- Ignoring points at interval boundaries
Trap Explanation:
PITFALL- Candidates often think points at end+1 are outside coverage, but event order matters.
Interviewer Note:
CONTEXT- Tests handling of edge cases with zero-length intervals and event ordering.
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