Scheduling algorithm (SCAN, LOOK) in LLD - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to select the initial direction for the SCAN algorithm.

LLD

direction = [1]  # Choose initial head movement direction

Drag options to blanks, or click blank then click option'

A"down"

B"up"

C"right"

D"left"

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing a direction unrelated to disk tracks like 'up' or 'down'.

The SCAN algorithm moves the disk head initially towards the right (higher track numbers) or left (lower track numbers). Commonly, it starts moving right.

2fill in blank

medium

Complete the code to find the next request to service in the LOOK algorithm.

LLD

next_request = min([r for r in requests if r > current_head], default=[1])

Drag options to blanks, or click blank then click option'

A-1

BNone

C0

Dcurrent_head

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 or -1 which may be valid track numbers and cause errors.

In LOOK, if no requests are ahead, min returns None to indicate no next request in that direction.

3fill in blank

hard

Fix the error in the code that updates the head position after servicing a request in SCAN.

LLD

current_head = [1]  # Update head to the serviced request

Drag options to blanks, or click blank then click option'

Anext_request

Brequests.pop()

Crequests[0]

Dcurrent_head + 1

Attempts:

3 left

💡 Hint

Common Mistakes

Using requests.pop() which removes but may not be the correct request.

Incrementing head by 1 regardless of request location.

The head should move to the position of the serviced request, which is stored in next_request.

4fill in blank

hard

Fill both blanks to complete the condition that reverses direction in SCAN when no requests remain in current direction.

LLD

if not any(r [1] current_head for r in requests):
    direction = [2]

Drag options to blanks, or click blank then click option'

A>

B<

C"left"

D"right"

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong comparison operators or wrong direction strings.

If no requests are greater than the current head, the direction reverses to left.

5fill in blank

hard

Fill all three blanks to complete the LOOK algorithm's main loop for servicing requests.

LLD

while requests:
    if direction == [1]:
        next_request = min([r for r in requests if r > current_head], default=None)
    else:
        next_request = max([r for r in requests if r < current_head], default=None)
    if next_request is None:
        direction = [2] if direction == [1] else [1]
        continue
    current_head = [3]
    requests.remove(next_request)

Drag options to blanks, or click blank then click option'

A"right"

B"left"

Cnext_request

Dcurrent_head

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing direction strings, not updating head correctly, or reversing direction incorrectly.

The LOOK algorithm moves right or left depending on direction, reverses when no requests remain in that direction, and updates the head to the next request.