Choosing the Right
Data Structure

Understanding the Importance of Choosing the Right Data Structure

Choosing the right data structure is a critical step in solving problems efficiently. Each data structure has specific strengths and trade-offs. Selecting the wrong one can lead to inefficient code, memory waste, and performance bottlenecks.

Factors to Consider When Choosing a Data Structure

• Access time: How fast can you retrieve an element?
• Insertion/Deletion: Do you need to add or remove frequently?
• Ordering: Do elements need to be stored in a particular order?
• Duplication: Should duplicates be allowed?
• Memory usage: Is the structure memory-efficient?

Example 1: When to Use an Array

Use an Array when you know the number of elements in advance and need fast access using indexes.

Initialize array A with size 5
Set A[0] = 10
Set A[1] = 20
Access A[1]  // returns 20

Output:

20

Question:

Why is an array not a good choice when you need to insert elements frequently in the middle?

Answer:

Because arrays require shifting elements when inserting in the middle, which is an O(n) operation.

Example 2: When to Use a List

Use a List (or Linked List) when you need frequent insertion and deletion, especially in the middle.

Create empty List L
Insert 10 at the beginning
Insert 20 at the end
Delete element at index 1

Output:

List contains: [10]

Question:

Is accessing the 4th element in a list efficient?

Answer:

No, in a linked list, accessing the nth element requires traversing from the head node, which takes O(n) time.

Example 3: When to Use a Set

Use a Set when you need to store unique elements only and care more about fast membership checks than ordering.

Create empty Set S
Add 10 to S
Add 20 to S
Add 10 to S again  // Ignored, as it's a duplicate
Check if 20 exists in S

Output:

Set contains: {10, 20}

Question:

Why is a set more efficient for membership checking than a list?

Answer:

Because sets are implemented using hash tables, and checking membership is typically O(1).

Example 4: When to Use a Stack

A Stack is ideal when you need Last In First Out (LIFO) behavior — such as undo operations or evaluating expressions.

Create empty Stack St
Push 10
Push 20
Pop top element  // returns 20
Peek top element  // returns 10

Output:

Popped: 20, Top: 10

Example 5: When to Use a Queue

A Queue is used when you need First In First Out (FIFO) behavior — such as task scheduling or buffering.

Create empty Queue Q
Enqueue 5
Enqueue 10
Dequeue element  // returns 5

Output:

Dequeued: 5

Example 6: When to Use a Map (or Dictionary)

A Map or Dictionary stores key-value pairs and is best for scenarios where you need to look up values based on unique keys.

Create empty Map M
Set M["name"] = "Alice"
Set M["age"] = 25
Access M["name"]  // returns "Alice"

Output:

Alice

Question:

When should you avoid using a map?

Answer:

When the number of elements is very small or when ordered data is critical, as maps do not guarantee order (unless using ordered variants).

Summary Table: Choosing the Right Data Structure

Data Structure	Use When	Time Complexity (Typical)
Array	Fast index-based access, fixed size	Access: O(1), Insert: O(n), Delete: O(n)
List	Frequent insert/delete, unknown size	Access: O(n), Insert/Delete: O(1)
Set	Unique values, fast membership	Insert/Check: O(1)
Stack	LIFO operations (Undo, Back)	Push/Pop: O(1)
Queue	FIFO operations (Tasks, Print Queue)	Enqueue/Dequeue: O(1)
Map	Key-value lookup	Access/Insert: O(1)

Key Takeaway

The choice of data structure dramatically affects the speed, memory usage, and maintainability of your code. Start by analyzing the operations your problem needs most — fast access, insertion, or lookup — and select the structure that aligns best with those needs.