Memory Layout Comparison Array vs Linked List in DSA Go - Interactive Comparison Practice

Practice - 5 Tasks

1fill in blank

easy

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

DSA Go

var numbers [[1]]int

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

A0

B1

C10

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 or 1 as array size when 5 is needed.

Confusing array size with slice length.

The array size is specified inside the square brackets. Here, 5 means the array has 5 elements.

2fill in blank

medium

Complete the code to define a linked list node struct with an integer value and a pointer to the next node.

DSA Go

type Node struct {
    value int
    next *[1]
}

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

ANode

Bint

CList

DPointer

Attempts:

3 left

💡 Hint

Common Mistakes

Using int or unrelated types for next pointer.

Forgetting the pointer symbol *.

The next field points to the next Node in the linked list, so its type is *Node.

3fill in blank

hard

Fix the error in the code to append a new node to the end of a linked list.

DSA Go

func appendNode(head *Node, val int) *Node {
    newNode := &Node{value: val}
    if head == nil {
        return newNode
    }
    current := head
    for current.next [1] nil {
        current = current.next
    }
    current.next = newNode
    return head
}

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

A<

B==

C!=

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' causes loop to stop immediately.

Using comparison operators like '<' or '>' on pointers.

The loop should continue while current.next is not nil to reach the last node.

4fill in blank

hard

Fill both blanks to create a slice from an array and iterate over it.

DSA Go

arr := [5]int{1, 2, 3, 4, 5}
slice := arr[[1]:[2]]
for i, v := range slice {
    fmt.Println(i, v)
}

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

A1

B0

C3

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Using 1 as start index misses the first element.

Using 5 as end index includes all elements.

The slice starts at index 0 and goes up to but not including index 3, so it includes elements 1, 2, and 3.

5fill in blank

hard

Fill all three blanks to create a map from string to int with a condition.

DSA Go

words := []string{"go", "code", "list", "array"}
lengths := map[string]int{}
for _, word := range words {
    if len(word) [1] [2] {
        lengths[[3]] = len(word)
    }
}

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

A>

B3

Cword

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' changes the condition.

Using a number or wrong variable as map key.

This code adds words longer than 3 characters to the map with their lengths.

Practice

1. Which of the following best describes the memory layout of an array compared to a linked list?

easy

A. Both array and linked list elements are scattered randomly in memory.

B. Both array and linked list elements are stored contiguously in memory.

C. Linked list elements are stored contiguously, but array elements are scattered in memory.

D. Array elements are stored in contiguous memory locations, while linked list nodes are scattered in memory.

Solution

1. Step 1: Understand array memory layout

   Arrays store elements in a continuous block of memory, one after another.

2. Step 2: Understand linked list memory layout

   Linked list nodes are allocated separately and linked via pointers, so they are scattered.

3. Final Answer:

   Array elements are stored in contiguous memory locations, while linked list nodes are scattered in memory. -> Option D

4. Quick Check:

   Array = contiguous, Linked list = scattered [OK]

Hint: Arrays are continuous; linked lists use pointers to scattered nodes [OK]

Common Mistakes:

• Thinking linked list nodes are stored contiguously
• Confusing array and linked list memory layouts
• Assuming both have same memory layout

2. Which Go syntax correctly declares an array of 5 integers?

easy

A. var arr []int = [5]

B. arr := []int{5}

C. var arr [5]int

D. arr := [5]int

Solution

1. Step 1: Recall Go array declaration syntax

   Arrays are declared with fixed size inside square brackets before the type, e.g., [5]int.

2. Step 2: Check each option

   A: var arr [5]int uses correct syntax. B: arr := []int{5} creates a slice with one element. C: var arr []int = [5] is invalid syntax. D: arr := [5]int is invalid syntax - missing composite literal {}.

3. Final Answer:

   var arr [5]int -> Option C

4. Quick Check:

   Array declaration = var arr [5]int [OK]

Hint: Array size goes inside brackets before type in Go [OK]

Common Mistakes:

• Using slice syntax instead of array syntax
• Placing size after type
• Incorrect initialization syntax

3. Consider this Go code snippet:

package main

import "fmt"

type Node struct {
    value int
    next  *Node
}

func main() {
    var head *Node
    head = &Node{value: 1}
    head.next = &Node{value: 2}
    head.next.next = &Node{value: 3}
    
    arr := [3]int{1, 2, 3}
    
    fmt.Println(arr)
    fmt.Println(head.value, head.next.value, head.next.next.value)
}

What will be the output?

medium

A. [1 2 3]
3 2 1

B. [1 2 3]
1 2 3

C. [1 2 3]
1 3 2

D. Compilation error

Solution

1. Step 1: Understand array print output

   Array arr contains [1, 2, 3], so fmt.Println(arr) prints [1 2 3].

2. Step 2: Understand linked list traversal print

   head.value = 1, head.next.value = 2, head.next.next.value = 3, so printing them in order prints '1 2 3'.

3. Final Answer:

   [1 2 3] 1 2 3 -> Option B

4. Quick Check:

   Array and linked list values match printed order [OK]

Hint: Print array and linked list values in order to verify [OK]

Common Mistakes:

• Confusing linked list node order
• Expecting commas in array print
• Assuming compilation error due to pointers

4. The following Go code attempts to create a linked list but has an error:

type Node struct {
    value int
    next  *Node
}

func main() {
    var head *Node
    head.value = 10
    head.next = nil
}

What is the error and how to fix it?

medium

A. head is nil pointer; initialize head before assigning fields

B. next field should be value, not pointer

C. value field must be a pointer type

D. No error; code runs fine

Solution

1. Step 1: Identify pointer initialization issue

   head is declared as *Node but not initialized, so it is nil (no memory allocated).

2. Step 2: Fix by allocating memory for head

   Use head = &Node{} before assigning head.value and head.next to avoid nil pointer dereference.

3. Final Answer:

   head is nil pointer; initialize head before assigning fields -> Option A

4. Quick Check:

   Nil pointer must be initialized before use [OK]

Hint: Always allocate memory for pointer before field access [OK]

Common Mistakes:

• Assigning fields on nil pointer
• Changing field types unnecessarily
• Ignoring runtime panic from nil dereference

5. You want to store 1 million integers and frequently insert and delete elements in the middle. Considering memory layout and performance, which data structure is better and why?

1. Array
2. Linked List

hard

A. Linked List, because scattered nodes make insertions and deletions faster despite poor cache usage

B. Linked List, because arrays cannot store large data

C. Array, because insertions and deletions are always faster in arrays

D. Array, because contiguous memory improves cache performance despite costly insertions

Solution

1. Step 1: Analyze insertion/deletion cost in arrays

   Arrays store data contiguously, so inserting or deleting in the middle requires shifting many elements, which is slow.

2. Step 2: Analyze linked list insertion/deletion

   Linked lists store nodes scattered but allow fast insert/delete by changing pointers without shifting elements.

3. Step 3: Consider memory and cache trade-offs

   Arrays have better cache performance due to contiguous memory, but linked lists are better for frequent middle insertions/deletions.

4. Final Answer:

   Linked List, because scattered nodes make insertions and deletions faster despite poor cache usage -> Option A

5. Quick Check:

   Frequent middle insert/delete favors linked list [OK]

Hint: Frequent middle insert/delete? Choose linked list despite cache cost [OK]

Common Mistakes:

• Assuming arrays always faster for insert/delete
• Ignoring shifting cost in arrays
• Thinking arrays can't store large data