Traversal Forward and Backward in DSA Go - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to traverse the slice forward and print each element.

DSA Go

for i := 0; i [1] len(numbers); i++ {
    fmt.Println(numbers[i])
}

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

A<

B>

C<=

D>=

Attempts:

3 left

💡 Hint

Common Mistakes

Using <= causes index out of range error.

Using > or >= will not enter the loop.

The loop should run from 0 up to but not including len(numbers), so the condition is i < len(numbers).

2fill in blank

medium

Complete the code to traverse the slice backward and print each element.

DSA Go

for i := len(numbers) - 1; i [1] 0; i-- {
    fmt.Println(numbers[i])
}

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

A<=

B>

C<

D>=

Attempts:

3 left

💡 Hint

Common Mistakes

Using > excludes the first element at index 0.

Using < or <= will not run the loop backward.

To traverse backward, loop from i = len(numbers) - 1 down to 0 inclusive, so the condition is i >= 0.

3fill in blank

hard

Fix the error in the backward traversal loop condition to include the first element.

DSA Go

for i := len(numbers) - 1; i [1] 0; i-- {
    fmt.Println(numbers[i])
}

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

A<=

B>=

C<

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using > excludes the first element at index 0.

Using < or <= will not traverse backward.

Using i >= 0 ensures the loop includes the first element at index 0.

4fill in blank

hard

Fill both blanks to create a forward traversal that skips the first element and stops before the last.

DSA Go

for i := [1]; i [2] len(numbers) - 1; i++ {
    fmt.Println(numbers[i])
}

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

A1

B0

C<

D<=

Attempts:

3 left

💡 Hint

Common Mistakes

Starting from 0 includes the first element.

Using <= includes the last element.

Start from index 1 to skip the first element, and loop while i is less than len(numbers) - 1 to stop before the last element.

5fill in blank

hard

Fill all three blanks to create a backward traversal that skips the last element and stops after the first.

DSA Go

for i := [1]; i [2] 0; i [3] {
    fmt.Println(numbers[i])
}

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

Alen(numbers) - 2

B>

Ci--

Dlen(numbers) - 1

Attempts:

3 left

💡 Hint

Common Mistakes

Starting from len(numbers) - 1 includes the last element.

Using >= includes the first element.

Forgetting to decrement i causes infinite loop.

Start from len(numbers) - 2 to skip the last element, loop while i > 0 to stop after the first, and decrement i each iteration.

Practice

1. What does "Traversal Forward and Backward" mean in the context of a doubly linked list?

easy

A. Visiting nodes from the start to the end and then from the end back to the start

B. Only visiting nodes from the start to the end

C. Only visiting nodes from the end to the start

D. Skipping nodes randomly during traversal

Solution

1. Step 1: Understand forward traversal

   Forward traversal means visiting nodes starting from the first node and moving to the last node.

2. Step 2: Understand backward traversal

   Backward traversal means visiting nodes starting from the last node and moving back to the first node.

3. Final Answer:

   Visiting nodes from the start to the end and then from the end back to the start -> Option A

4. Quick Check:

   Traversal forward and backward = visiting nodes both ways [OK]

Hint: Think of walking forward then turning back [OK]

Common Mistakes:

• Confusing forward traversal with backward traversal
• Thinking traversal only goes one way
• Assuming traversal skips nodes

2. Which of the following Go code snippets correctly traverses a doubly linked list forward?

easy

A. for node := head; node != nil; node = node.prev { fmt.Println(node.value) }

B. for node := head; node != nil; node = node.next { fmt.Println(node.value) }

C. for node := tail; node != nil; node = node.next { fmt.Println(node.value) }

D. for node := tail; node != nil; node = node.prev { fmt.Println(node.value) }

Solution

1. Step 1: Identify forward traversal start point

   Forward traversal starts at the head (first node).

2. Step 2: Identify correct pointer for forward traversal

   Moving forward uses the next pointer, so node = node.next is correct.

3. Final Answer:

   for node := head; node != nil; node = node.next { fmt.Println(node.value) } -> Option B

4. Quick Check:

   Forward traversal uses head and next pointer [OK]

Hint: Forward traversal starts at head and uses next [OK]

Common Mistakes:

• Starting traversal at tail for forward direction
• Using prev pointer for forward traversal
• Confusing next and prev pointers

3. What is the output of the following Go code snippet that traverses a doubly linked list backward?

type Node struct {
  value int
  prev  *Node
  next  *Node
}

func main() {
  n1 := &Node{value: 1}
  n2 := &Node{value: 2}
  n3 := &Node{value: 3}
  n1.next = n2
  n2.prev = n1
  n2.next = n3
  n3.prev = n2

  for node := n3; node != nil; node = node.prev {
    fmt.Print(node.value, " ")
  }
}

medium

A. 3 1 2

B. 1 2 3

C. 3 2 1

D. 2 3 1

Solution

1. Step 1: Understand backward traversal start

   The loop starts at n3 (value 3) and moves backward using prev pointer.

2. Step 2: Trace the loop values

   First prints 3, then moves to n2 (2), prints 2, then moves to n1 (1), prints 1, then stops at nil.

3. Final Answer:

   3 2 1 -> Option C

4. Quick Check:

   Backward traversal prints 3 2 1 [OK]

Hint: Backward traversal prints values from tail to head [OK]

Common Mistakes:

• Confusing order of printing
• Starting traversal at head for backward
• Using next pointer instead of prev

4. Identify the error in the following Go code that attempts to traverse a doubly linked list backward:

for node := head; node != nil; node = node.prev {
  fmt.Println(node.value)
}

medium

A. Starting traversal at head but moving backward with prev pointer

B. Using fmt.Println instead of fmt.Print

C. Missing initialization of node variable

D. Loop condition should be node == nil

Solution

1. Step 1: Check traversal start and direction

   The code starts at head (first node) but moves backward using prev pointer, which is incorrect because head.prev is nil.

2. Step 2: Identify correct traversal logic

   Backward traversal should start at tail, not head, when moving with prev pointer.

3. Final Answer:

   Starting traversal at head but moving backward with prev pointer -> Option A

4. Quick Check:

   Backward traversal must start at tail [OK]

Hint: Backward traversal starts at tail, not head [OK]

Common Mistakes:

• Starting backward traversal at head
• Confusing loop condition
• Ignoring pointer directions

5. Given a doubly linked list, how would you print all elements first forward and then backward without repeating the last element twice in Go?

hard

A. Traverse backward printing all nodes, then traverse forward starting from head to tail

B. Traverse forward printing all nodes, then traverse backward starting from tail to head

C. Traverse forward printing all nodes, then traverse backward starting from head.prev to tail

D. Traverse forward printing all nodes, then traverse backward starting from tail.prev to head

Solution

1. Step 1: Traverse forward and print all nodes

   Start from head and print each node until tail inclusive.

2. Step 2: Traverse backward starting from tail.prev to avoid duplicate tail

   Start backward traversal from tail.prev to head to avoid printing tail twice.

3. Final Answer:

   Traverse forward printing all nodes, then traverse backward starting from tail.prev to head -> Option D

4. Quick Check:

   Skip last node in backward traversal to avoid duplicate print [OK]

Hint: Skip tail in backward traversal to avoid duplicate print [OK]

Common Mistakes:

• Printing tail twice by starting backward at tail
• Starting backward traversal incorrectly
• Confusing traversal directions