LRANGE for reading elements in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What does this LRANGE command return?

Given a Redis list mylist with elements ["a", "b", "c", "d", "e"], what is the output of the command LRANGE mylist 1 3?

Redis

LRANGE mylist 1 3

A ["a", "b", "c"]

B ["b", "c", "d"]

C ["c", "d", "e"]

D ["b", "c", "d", "e"]

💡 Hint

Remember that LRANGE uses zero-based indexing and includes both start and end positions.

LRANGE returns elements from the start index to the end index inclusive. Index 1 is 'b', index 3 is 'd', so the result is ['b', 'c', 'd'].

❓ query_result

intermediate

What is the output of LRANGE with negative indices?

If mylist contains ["x", "y", "z", "w"], what does LRANGE mylist -3 -1 return?

Redis

LRANGE mylist -3 -1

A ["y", "z", "w"]

B ["x", "y", "z"]

C ["w"]

D ["z", "w"]

💡 Hint

Negative indices count from the end of the list, starting at -1 for the last element.

Index -3 corresponds to 'y', and -1 corresponds to 'w'. LRANGE returns elements from 'y' to 'w' inclusive.

📝 Syntax

advanced

Which LRANGE command is syntactically correct?

Identify the syntactically valid LRANGE command to get elements from index 2 to 4 from list mylist.

A LRANGE mylist 2-4

B LRANGE mylist 2,4

C LRANGE mylist (2 4)

D LRANGE mylist 2 4

💡 Hint

LRANGE syntax requires the key followed by two separate integer arguments for start and stop.

Only option D uses the correct syntax: LRANGE key start stop with spaces separating arguments.

❓ optimization

advanced

Efficiently reading the last 5 elements of a large list

You have a Redis list biglist with 1 million elements. Which LRANGE command efficiently retrieves the last 5 elements?

A LRANGE biglist 999995 999999

B LRANGE biglist 0 4

C LRANGE biglist -5 -1

D LRANGE biglist 999995 -1

💡 Hint

Negative indices are a convenient way to access elements from the end without calculating exact positions.

Using negative indices like -5 to -1 directly accesses the last 5 elements without needing to know the list length.

🧠 Conceptual

expert

What happens if LRANGE start index is greater than end index?

Consider a Redis list mylist with elements ["p", "q", "r"]. What is the result of LRANGE mylist 2 1?

A An empty list []

B A syntax error

C Returns elements from index 1 to 2

D Returns all elements

💡 Hint

LRANGE returns elements from start to end index inclusive, but start must be less or equal to end.

If start index is greater than end index, LRANGE returns an empty list without error.