LLD - Design — Elevator System
In the LOOK disk scheduling algorithm, if the head starts at position 30 and the requests are at [5, 15, 25, 35, 45, 55], what is the order of servicing requests if the head moves towards lower track numbers first?
In the LOOK disk scheduling algorithm, if the head starts at position 30 and the requests are at [5, 15, 25, 35, 45, 55], what is the order of servicing requests if the head moves towards lower track numbers first?
medium📝 Analysis Q5 of 15
Step-by-Step Solution
Solution:
Step 1: Determine head movement direction
The head starts at 30 and moves towards lower track numbers first.Step 2: Service requests less than 30 in descending order
Requests less than 30 are 25, 15, and 5, serviced in order: 25, 15, 5.Step 3: Reverse direction and service remaining requests
After reaching the lowest request (5), the head reverses and services requests greater than 30 in ascending order: 35, 45, 55.Final Answer:
[30, 25, 15, 5, 35, 45, 55] -> Option BQuick Check:
Head moves down first, then up servicing requests accordingly [OK]
Quick Trick: LOOK moves only as far as last request in direction [OK]
Common Mistakes:
MISTAKES- Servicing requests out of head movement order
- Assuming head moves to disk end regardless of requests
- Not reversing direction after last request
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