Interval Graph Scheduling

Interval Graph Scheduling problems involve allocating rooms or venues to events that have fixed start and end times. The minimum number of rooms needed equals the maximum number of overlapping intervals (maximum clique size in interval graph).

10Worksheets
200+Practice Questions
IntermediateDifficulty
2-3 hoursHours to Master

Introduction to Interval Graph Scheduling

Interval Graph Scheduling problems involve allocating rooms or venues to events that have fixed start and end times. The minimum number of rooms needed equals the maximum number of overlapping intervals (maximum clique size in interval graph).

Prerequisites

Interval overlap Maximum overlap detection Sweep line algorithm Resource allocation
Why This Matters: Interval Graph problems appear in 1-2 questions in Banking PO and SSC exams. They test overlap detection and resource allocation.

How to Solve Interval Graph Scheduling Problems

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Step 1: List all events with start and end times

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Step 2: Sort all time points (starts and ends)

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Step 3: Sweep through timeline, count active events

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Step 4: Track maximum number of simultaneously active events

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Step 5: This maximum = minimum rooms needed

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Step 6: Answer with number of rooms

Pro Strategy: Use sweep line: sort events by start time, track end times. Maximum concurrent events is answer.

Example Problem

Example: Events: A(9-10), B(9:30-11), C(10-12), D(11-1). Minimum rooms? Solution: Step 1: Time points: 9(A start), 9:30(B start), 10(A end, C start), 11(B end, D start), 12(C end), 1(D end) Step 2: Sweep: 9→1 active (A); 9:30→2 (A,B); 10→A ends, C starts → still 2 (B,C); 11→B ends, D starts → 2 (C,D); 12→C ends →1 (D); 1→end Step 3: Max overlap = 2 Answer: 2 rooms

Pro Tips & Tricks

  • Sort all events by start time
  • Use min-heap to track end times of active events
  • When new event starts, remove ended events from heap
  • Maximum heap size = maximum overlap
  • This equals chromatic number of interval graph

Shortcut Methods to Solve Faster

Minimum rooms = maximum number of overlapping intervals
If no overlaps, 1 room
If all overlap at one point, n rooms
Check peak time for maximum demand

Common Mistakes to Avoid

Counting total events instead of concurrent events
Forgetting that end times are exclusive (if one ends at 10 and another starts at 10, can use same room)
Not sorting events correctly
Using average instead of maximum

Exam Importance

Interval Graph Scheduling is an important topic for various competitive exams. Here's how frequently it appears:

SSC CGL
1-2 questions
BANKING PO
1-2 questions
RAILWAYS RRB
1-2 questions
INSURANCE
1-2 questions

Ready to Master Interval Graph Scheduling?

Start with Worksheet 1 and work your way up to expert level! Each worksheet includes:

20 practice questions
Detailed solutions
Step-by-step explanations
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