Arrays vs Other Data Structures When to Choose Arrays in DSA Go - Compare & Choose

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of array vs slice length after append

What is the output of the following Go code snippet?

DSA Go

package main
import "fmt"
func main() {
    arr := [3]int{1, 2, 3}
    slice := arr[:]
    slice = append(slice, 4)
    fmt.Println(len(arr), len(slice))
}

A 4 4

B 3 4

C 3 3

D 4 3

💡 Hint

Remember arrays have fixed size, slices can grow.

The array has fixed length 3. The slice initially references the array but append creates a new underlying array with length 4. So arr length is 3, slice length is 4.

🧠 Conceptual

intermediate

When to prefer arrays over linked lists?

Which scenario best justifies choosing arrays instead of linked lists?

A When memory usage must be minimal and flexible

B When you need frequent insertions and deletions in the middle

C When you want to avoid resizing overhead

D When you need fast random access to elements by index

💡 Hint

Think about how arrays store elements contiguously.

Arrays store elements contiguously, allowing O(1) access by index. Linked lists require traversal, so arrays are better for fast random access.

❓ Predict Output

advanced

Result of array modification via pointer

What is the output of this Go program?

DSA Go

package main
import "fmt"
func modify(arr *[3]int) {
    (*arr)[0] = 10
}
func main() {
    a := [3]int{1, 2, 3}
    modify(&a)
    fmt.Println(a)
}

A [10 2 3]

B [1 2 3]

C [0 2 3]

D Compilation error

💡 Hint

Passing array pointer allows modification of original array.

The function receives a pointer to the array and modifies the first element. This change reflects in the original array, so output is [10 2 3].

🔧 Debug

advanced

Identify the error in array copying

What error occurs when running this Go code?

DSA Go

package main
func main() {
    var a [3]int = [3]int{1, 2, 3}
    var b [4]int = a
}

A cannot use a (type [3]int) as type [4]int in assignment

B index out of range panic

C no error, code runs fine

D syntax error: missing semicolon

💡 Hint

Arrays of different sizes are distinct types in Go.

Arrays with different sizes are different types in Go. Assigning [3]int to [4]int causes a compile-time type mismatch error.

🚀 Application

expert

Choosing data structure for fixed-size, fast access, and minimal memory

You need to store a fixed number of elements with fast access by index and minimal memory overhead. Which data structure is best?

A Binary Search Tree

B Linked List

C Array

D Hash Map

💡 Hint

Consider memory layout and access speed.

Arrays have fixed size, store elements contiguously, and provide O(1) access by index with minimal overhead compared to other structures.

Practice

1. Which of the following is the best reason to choose an array over other data structures like linked lists or hash maps?

easy

A. When you want a flexible size that grows automatically

B. When you need to frequently insert or delete elements in the middle

C. When you want to store key-value pairs

D. When you need fast access to elements by index

Solution

1. Step 1: Understand array access speed

   Arrays allow direct access to elements using their index, which is very fast (constant time).

2. Step 2: Compare with other data structures

   Linked lists are slower for access by index, hash maps store key-value pairs, and dynamic structures grow automatically but may have overhead.

3. Final Answer:

   When you need fast access to elements by index -> Option D

4. Quick Check:

   Fast index access = Array = A [OK]

Hint: Arrays give quick access by position, unlike others [OK]

Common Mistakes:

• Choosing arrays for frequent insertions/deletions
• Confusing arrays with key-value stores
• Assuming arrays grow automatically

2. Which of the following is the correct way to declare an array of 5 integers in Go?

easy

A. var arr [5]int

B. arr := []int{5}

C. var arr = make([]int, 5)

D. arr := [5]int

Solution

1. Step 1: Recall Go array declaration syntax

   Arrays in Go are declared with fixed size using syntax: var name [size]type.

2. Step 2: Analyze options

   var arr [5]int uses correct syntax for fixed-size array. arr := []int{5} is a slice literal with one element 5. var arr = make([]int, 5) creates a slice with length 5, not an array. arr := [5]int is invalid syntax.

3. Final Answer:

   var arr [5]int -> Option A

4. Quick Check:

   Fixed size array = var arr [5]int [OK]

Hint: Fixed size arrays use var name [size]type in Go [OK]

Common Mistakes:

• Using slice syntax instead of array syntax
• Confusing make() with array creation
• Incorrect literal syntax for arrays

3. What will be the output of the following Go code snippet?

package main
import "fmt"
func main() {
    arr := [3]int{10, 20, 30}
    fmt.Println(arr[1])
}

medium

A. 10

B. 20

C. 30

D. Index out of range error

Solution

1. Step 1: Identify array elements and indexing

   The array has elements [10, 20, 30] at indices 0, 1, and 2 respectively.

2. Step 2: Access element at index 1

   arr[1] refers to the second element, which is 20.

3. Final Answer:

   20 -> Option B

4. Quick Check:

   arr[1] = 20 [OK]

Hint: Remember arrays start at index 0 in Go [OK]

Common Mistakes:

• Confusing index 1 with first element
• Expecting runtime error for valid index
• Misreading array initialization

4. Consider the following Go code snippet. What is the error and how to fix it?

package main
import "fmt"
func main() {
    arr := [3]int{1, 2, 3}
    arr[3] = 4
    fmt.Println(arr)
}

medium

A. Index out of range error; fix by using valid index 0 to 2

B. Syntax error; fix by declaring arr as slice

C. No error, output: [1 2 3 4]

D. Compile error; fix by increasing array size to 4

Solution

1. Step 1: Identify the invalid index access

   Array size is 3, valid indices are 0, 1, 2. Accessing arr[3] is out of range.

2. Step 2: Fix the error

   Use indices within 0 to 2 or declare a larger array if needed.

3. Final Answer:

   Index out of range error; fix by using valid index 0 to 2 -> Option A

4. Quick Check:

   Array index must be within size [OK]

Hint: Array indices go from 0 to size-1 only [OK]

Common Mistakes:

• Trying to assign outside array bounds
• Confusing array size with slice length
• Ignoring runtime panic from invalid index

5. You need to store a fixed number of sensor readings that will not change in size and require fast access by position. Which data structure should you choose and why?

medium

A. Use a linked list because it allows easy insertion and deletion

B. Use a hash map because it provides key-value access

C. Use an array because it has fixed size and fast index access

D. Use a slice because it automatically resizes

Solution

1. Step 1: Analyze requirements

   The size is fixed and will not change, and fast access by position is needed.

2. Step 2: Match data structure properties

   Arrays have fixed size and provide constant time access by index. Linked lists are slower for access, hash maps are for key-value pairs, slices resize dynamically which is unnecessary here.

3. Final Answer:

   Use an array because it has fixed size and fast index access -> Option C

4. Quick Check:

   Fixed size + fast access = Array = D [OK]

Hint: Fixed size and fast access? Choose array [OK]

Common Mistakes:

• Choosing linked list for fixed size data
• Using hash map without key-value need
• Picking slice when resizing is not required