Traversal of Circular Linked List in DSA Go - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a circular linked list?

A circular linked list is a linked list where the last node points back to the first node, forming a circle. There is no null at the end.

beginner

How do you know when to stop traversing a circular linked list?

You stop when you reach the starting node again after moving forward. This means you have visited all nodes once.

intermediate

Why can't we use 'null' to stop traversal in a circular linked list?

Because the last node points back to the first node, there is no null to indicate the end. We must track the start node to stop.

beginner

Show the basic steps to traverse a circular linked list.

1. Start at the head node.
2. Visit the current node.
3. Move to the next node.
4. Repeat until you reach the head node again.

intermediate

What is a common mistake when traversing a circular linked list?

A common mistake is to forget to check if the current node is the start node again, causing an infinite loop.

In a circular linked list, what does the last node point to?

A Null

B The first node

C A random node

D Itself

The last node in a circular linked list points back to the first node, creating a circle.

When traversing a circular linked list, how do you know when to stop?

A When current node is the start node again

B When current node is null

C After visiting 10 nodes

D When next node is null

Traversal stops when you reach the start node again, meaning you completed one full circle.

What happens if you forget to check for the start node during traversal?

A You skip nodes

B Traversal stops early

C Infinite loop occurs

D Program crashes immediately

Without checking for the start node, traversal never ends and causes an infinite loop.

Which of these is NOT true about circular linked lists?

A They have no null at the end

B They can be traversed starting from any node

C The last node points to the first node

D They always have a fixed size

Circular linked lists can grow or shrink; they do not have a fixed size.

What is the first step in traversing a circular linked list?

A Start at the head node

B Delete the first node

C Check if next node is null

D Move to the last node

Traversal always starts at the head (or any chosen start) node.

Explain how to traverse a circular linked list safely without causing an infinite loop.

Think about how to know when you have seen all nodes once.

Describe the difference between traversing a normal linked list and a circular linked list.

Focus on how the end of the list is marked.

Practice

1. What is the main difference between a circular linked list and a regular singly linked list?

easy

A. In a circular linked list, the last node points back to the first node.

B. In a circular linked list, nodes have two pointers instead of one.

C. In a circular linked list, nodes are stored in an array.

D. In a circular linked list, the first node points to null.

Solution

1. Step 1: Understand the structure of a circular linked list

   A circular linked list connects the last node back to the first node, forming a circle.

2. Step 2: Compare with a regular singly linked list

   A regular singly linked list ends with a node pointing to null, not back to the first node.

3. Final Answer:

   In a circular linked list, the last node points back to the first node. -> Option A

4. Quick Check:

   Circular list loops back = D [OK]

Hint: Last node points to first node in circular list [OK]

Common Mistakes:

• Thinking circular list nodes have two pointers
• Confusing circular list with doubly linked list
• Assuming last node points to null

2. Which of the following Go code snippets correctly starts traversal of a circular linked list from the head node?

easy

A. current := head
for current != head {
fmt.Println(current.data)
current = current.next
}

B. current := head
for current.next != nil {
fmt.Println(current.data)
current = current.next
}

C. current := head
for current != nil {
fmt.Println(current.data)
current = current.next
if current == head {
break
}
}

D. current := head
for current != nil {
fmt.Println(current.data)
current = current.next
}

Solution

1. Step 1: Identify correct loop condition for circular list

   Traversal must stop when current returns to head to avoid infinite loop.

2. Step 2: Check code options

   current := head for current != nil { fmt.Println(current.data) current = current.next if current == head { break } } uses a break when current equals head, correctly stopping traversal.

3. Final Answer:

   current := head for current != nil { fmt.Println(current.data) current = current.next if current == head { break } } -> Option C

4. Quick Check:

   Stop when current == head = A [OK]

Hint: Stop traversal when current node equals head [OK]

Common Mistakes:

• Using nil as stop condition in circular list
• Not breaking loop causing infinite traversal
• Incorrect loop condition skipping nodes

3. What will be the output of the following Go code snippet that traverses a circular linked list with nodes containing values 10, 20, 30?

type Node struct {
    data int
    next *Node
}

func main() {
    n1 := &Node{data: 10}
    n2 := &Node{data: 20}
    n3 := &Node{data: 30}
    n1.next = n2
    n2.next = n3
    n3.next = n1

    current := n1
    for {
        fmt.Print(current.data, " ")
        current = current.next
        if current == n1 {
            break
        }
    }
}

medium

A. 20 30 10

B. 10 20 30

C. 10 20 30 10

D. Runtime error

Solution

1. Step 1: Understand the circular linked list setup

   Nodes 10 -> 20 -> 30 -> back to 10 form a circle.

2. Step 2: Trace the loop output

   Loop prints current.data then moves to next. Stops when current == n1 again, so prints 10, 20, 30 once.

3. Final Answer:

   10 20 30 -> Option B

4. Quick Check:

   Print nodes once before loop breaks = C [OK]

Hint: Print until current equals start node again [OK]

Common Mistakes:

• Printing extra node after loop break
• Starting traversal from wrong node
• Confusing output order

4. The following Go code attempts to traverse a circular linked list but causes an infinite loop. What is the error?

current := head
for current != nil {
    fmt.Println(current.data)
    current = current.next
}

medium

A. The code should use a for-range loop instead.

B. The code should print after updating current.

C. The list is not circular, so nil check is correct.

D. The loop condition should check if current equals head to stop.

Solution

1. Step 1: Analyze loop condition for circular list

   Checking current != nil never becomes false in circular list, causing infinite loop.

2. Step 2: Correct stopping condition

   Loop should stop when current returns to head node to avoid infinite traversal.

3. Final Answer:

   The loop condition should check if current equals head to stop. -> Option D

4. Quick Check:

   Stop when current == head to avoid infinite loop [OK]

Hint: Use current == head to break loop in circular list [OK]

Common Mistakes:

• Using nil as loop end in circular list
• Not breaking loop causing infinite print
• Misplacing print statement

5. Given a circular linked list where each node contains an integer, write a Go function to find the sum of all node values. Which approach correctly handles traversal without infinite looping?

hard

A. Start from head, add node data, move to next, stop when current equals head again.

B. Start from head, add node data, move to next, stop when current is nil.

C. Use recursion without base case to sum nodes.

D. Traverse nodes twice to ensure all are counted.

Solution

1. Step 1: Understand traversal in circular linked list

   Traversal must stop when current node equals head again to avoid infinite loop.

2. Step 2: Summation logic

   Start at head, add each node's data to sum, move to next node, stop when back at head.

3. Final Answer:

   Start from head, add node data, move to next, stop when current equals head again. -> Option A

4. Quick Check:

   Stop at head to sum all nodes once [OK]

Hint: Stop traversal when current equals head to sum nodes [OK]

Common Mistakes:

• Stopping at nil causing infinite loop
• Using recursion without base case
• Traversing nodes multiple times