Arrays vs Other Data Structures When to Choose Arrays in DSA Go - Interactive Comparison Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare an array of 5 integers in Go.

DSA Go

var numbers [[1]]int

Drag options to blanks, or click blank then click option'

A5

B10

C0

D3

Attempts:

3 left

💡 Hint

Common Mistakes

Using parentheses instead of square brackets.

Forgetting to specify the size of the array.

The code declares an array named numbers with 5 elements of type int.

2fill in blank

medium

Complete the code to access the third element of the array named data.

DSA Go

value := data[[1]]

Drag options to blanks, or click blank then click option'

A1

B3

C2

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using 3 as the index which is actually the fourth element.

Using 1 or 0 which point to earlier elements.

Array indices in Go start at 0, so the third element is at index 2.

3fill in blank

hard

Fix the error in the code to append an element to a slice named items.

DSA Go

items = append(items, [1])

Drag options to blanks, or click blank then click option'

Aitems

Blen(items)

Cappend

DnewItem

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the slice itself as the element to append.

Passing the function name instead of a value.

The append function adds the value newItem to the slice items.

4fill in blank

hard

Fill both blanks to create a slice from an array named arr that includes elements from index 1 up to but not including index 3.

DSA Go

slice := arr[[1]:[2]]

Drag options to blanks, or click blank then click option'

A1

B3

C0

D4

Attempts:

3 left

💡 Hint

Common Mistakes

Using the same value for start and end which results in an empty slice.

Using an end index that is out of range.

Slicing syntax arr[start:end] includes elements from start up to but not including end. So arr[1:3] includes elements at indices 1 and 2.

5fill in blank

hard

Fill all three blanks to create a map from strings to integers with keys from a slice named keys and values from a slice named vals.

DSA Go

result := make(map[string]int)
for i := 0; i < len([1]); i++ {
    result[[2][i]] = [3][i]
}

Drag options to blanks, or click blank then click option'

Akeys

Bvals

Attempts:

3 left

💡 Hint

Common Mistakes

Using vals length for the loop which may cause index errors if lengths differ.

Mixing keys and vals in the map assignment.

The loop runs over the length of keys. For each index i, it sets result[keys[i]] = vals[i] to build the map.

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