LINDEX for position access in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output of LINDEX for a valid positive index?

Given a Redis list mylist with elements ["apple", "banana", "cherry"], what is the output of LINDEX mylist 1?

Redis

LINDEX mylist 1

A "banana"

B "apple"

C "cherry"

D nil

💡 Hint

Remember that Redis lists are zero-indexed, so index 1 is the second element.

LINDEX returns the element at the specified zero-based index. Index 1 corresponds to the second element, which is "banana".

❓ query_result

intermediate

What does LINDEX return for a negative index?

Given a Redis list colors with elements ["red", "green", "blue", "yellow"], what is the output of LINDEX colors -2?

Redis

LINDEX colors -2

A "blue"

B "yellow"

C "green"

D nil

💡 Hint

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

Index -1 is the last element "yellow", so -2 is the second last element "blue".

📝 Syntax

advanced

Which LINDEX command syntax is correct?

Which of the following Redis commands correctly uses LINDEX to get the first element of list tasks?

A LINDEX tasks

B LINDEX tasks 0

C LINDEX 0 tasks

D LINDEX tasks -0

💡 Hint

LINDEX requires the key first, then the index as an integer.

The correct syntax is LINDEX key index. Option B follows this format with index 0 for the first element.

❓ query_result

advanced

What is the output when LINDEX index is out of range?

Given a Redis list numbers with elements ["one", "two", "three"], what is the output of LINDEX numbers 5?

Redis

LINDEX numbers 5

A Error: index out of range

B "three"

C nil

D "five"

💡 Hint

If the index is outside the list range, Redis returns nil.

Since index 5 is beyond the last element (index 2), Redis returns nil indicating no element found.

🧠 Conceptual

expert

How does LINDEX handle concurrent modifications?

If a Redis list queue is modified (elements added or removed) by other clients while a client runs LINDEX queue 2, what can be said about the returned value?

A LINDEX returns a random element from the list if concurrent modifications happen.

B LINDEX always returns the element that was at index 2 when the list was first created, ignoring changes.

C LINDEX blocks until no other clients modify the list, then returns the element at index 2.

D LINDEX returns the element at index 2 at the exact time of the command execution, reflecting any concurrent changes.

💡 Hint

Think about how Redis commands are atomic and reflect the current state at execution.

Redis commands are atomic and see the list state at the moment of execution, so LINDEX returns the element at index 2 at that time, including any concurrent changes.