Hash Map vs Array vs Linked List for Lookup in DSA C - Key Differences

Recall & Review

beginner

What is the average time complexity for lookup in a Hash Map?

The average time complexity for lookup in a Hash Map is O(1), meaning it can find an element very quickly using a key.

beginner

How does lookup work in an Array?

Lookup in an Array is O(1) if you know the index because you can directly access the element. But if you search by value, it is O(n) because you may need to check each element.

beginner

Why is lookup in a Linked List slower than in an Array or Hash Map?

Lookup in a Linked List is O(n) because you must start at the head and check each node one by one until you find the target.

intermediate

What is a key advantage of using a Hash Map over an Array or Linked List for lookup?

A Hash Map provides fast lookup by key with average O(1) time, which is much faster than searching through an Array or Linked List when you don't know the index.

intermediate

When might you prefer using an Array over a Hash Map or Linked List for lookup?

You might prefer an Array when you need fast access by index and the data size is fixed or small, because Arrays use less memory and have simple structure.

What is the average time complexity of lookup in a Hash Map?

A O(1)

B O(n)

C O(log n)

D O(n log n)

Hash Maps use keys to directly access values, making average lookup time O(1).

If you want to find a value in an unsorted Array by searching each element, what is the time complexity?

A O(n)

B O(log n)

C O(1)

D O(n^2)

You may need to check each element, so the time is O(n).

Which data structure requires checking nodes one by one for lookup?

A Hash Map

B Array

C Binary Search Tree

D Linked List

Linked Lists store elements in nodes connected by pointers, so you check nodes one by one.

Which data structure provides fastest lookup by index?

A Hash Map

B Linked List

C Array

D Stack

Arrays allow direct access by index in O(1) time.

When is a Hash Map less efficient than an Array for lookup?

A When data is unsorted

B When you know the exact index

C When data is large

D When keys are strings

If you know the index, Array lookup is faster and simpler than Hash Map.

Explain the differences in lookup time complexity between Hash Map, Array, and Linked List.

Think about how each data structure accesses elements.

Describe scenarios where you would choose an Array, Linked List, or Hash Map for lookup operations.

Consider speed and type of access needed.