[Solved] You have a disk with size 200 tracks and requests at [10, 50, 120, 180].... What is the total head movement if the head moves towards lower track numbers first? | LLD

LLD - Design — Elevator System

You have a disk with size 200 tracks and requests at [10, 50, 120, 180]. The head is at 100 and moves using LOOK algorithm. What is the total head movement if the head moves towards lower track numbers first?

A260 tracks

B160 tracks

C180 tracks

D120 tracks

Step-by-Step Solution

Solution:

Step 1: Initial direction to lower tracks
Lower requests: 50, 10. Path: 100 -> 50 (50 tracks), 50 -> 10 (40 tracks). Subtotal: 90.
Step 2: Reverse direction to higher tracks
Higher requests: 120, 180. Path: 10 -> 120 (110 tracks), 120 -> 180 (60 tracks). Subtotal: 170.
Step 3: Total head movement
90 + 170 = 260 tracks.
Final Answer:
260 tracks -> Option A
Quick Check:
Sum of |current - next| over servicing sequence [OK]

Quick Trick: Sum distances in servicing order: 100-50-10-120-180 [OK]

Common Mistakes:

MISTAKES

Including disk edges in LOOK movement
Adding extra distances beyond last requests
Misordering request servicing

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More LLD Quizzes

What is the total head movement if the head moves towards lower track numbers first?

Step 1: Initial direction to lower tracks

Step 2: Reverse direction to higher tracks

Step 3: Total head movement

Final Answer:

Quick Check:

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