Search for a Value in Linked List in DSA C++ - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to return true if the value is found in the linked list.

DSA C++

bool search(Node* head, int target) {
    Node* current = head;
    while (current != nullptr) {
        if (current->data == [1]) {
            return true;
        }
        current = current->next;
    }
    return false;
}

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

Ahead

Btarget

Ccurrent

Dnullptr

Attempts:

3 left

💡 Hint

Common Mistakes

Comparing current->data with head instead of target.

Using nullptr in the comparison.

Comparing with current pointer instead of data.

The function compares each node's data with the target value to find a match.

2fill in blank

medium

Complete the code to move to the next node in the linked list.

DSA C++

bool search(Node* head, int target) {
    Node* current = head;
    while (current != nullptr) {
        if (current->data == target) {
            return true;
        }
        current = [1];
    }
    return false;
}

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

Ahead->next

Bnullptr

Ctarget->next

Dcurrent->next

Attempts:

3 left

💡 Hint

Common Mistakes

Using head->next instead of current->next.

Using target->next which is invalid.

Assigning nullptr which stops traversal.

To traverse the list, move current to current->next each time.

3fill in blank

hard

Fix the error in the condition to check if the list is empty.

DSA C++

bool search(Node* head, int target) {
    if (head == [1]) {
        return false;
    }
    Node* current = head;
    while (current != nullptr) {
        if (current->data == target) {
            return true;
        }
        current = current->next;
    }
    return false;
}

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

Anullptr

B0

Chead

Dtarget

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 instead of nullptr.

Comparing head with itself.

Comparing head with target value.

An empty list is indicated by head being nullptr, not 0 or other values.

4fill in blank

hard

Fill both blanks to create a function that returns the node containing the target value or nullptr if not found.

DSA C++

Node* searchNode(Node* head, int target) {
    Node* current = head;
    while (current != [1]) {
        if (current->data == [2]) {
            return current;
        }
        current = current->next;
    }
    return nullptr;
}

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

Anullptr

Bhead

Ctarget

Dcurrent

Attempts:

3 left

💡 Hint

Common Mistakes

Using head instead of nullptr in the loop condition.

Comparing current->data with head or current instead of target.

The loop continues until current is nullptr, and compares current->data with target.

5fill in blank

hard

Fill all three blanks to create a function that counts how many times the target value appears in the linked list.

DSA C++

int countOccurrences(Node* head, int target) {
    int count = 0;
    Node* current = [1];
    while (current != [2]) {
        if (current->data == [3]) {
            count++;
        }
        current = current->next;
    }
    return count;
}

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

Ahead

Bnullptr

Ctarget

Dcount

Attempts:

3 left

💡 Hint

Common Mistakes

Starting from nullptr instead of head.

Looping until head instead of nullptr.

Comparing data with count variable.

Start from head, loop until current is nullptr, and compare current->data with target to count matches.

Practice

1. What is the main purpose of searching for a value in a linked list?

easy

A. To add a new node at the end of the list

B. To find if a specific value exists in the list

C. To delete the first node of the list

D. To reverse the order of nodes in the list

Solution

1. Step 1: Understand the search operation

   Searching in a linked list means checking each node to see if it contains the value we want.

2. Step 2: Identify the goal of searching

   The goal is to find whether the value exists anywhere in the list, not to modify the list.

3. Final Answer:

   To find if a specific value exists in the list -> Option B

4. Quick Check:

   Search means find value presence = To find if a specific value exists in the list [OK]

Hint: Search means check each node for the value [OK]

Common Mistakes:

• Confusing search with insertion or deletion
• Thinking search changes the list
• Assuming search reverses the list

2. Which of the following is the correct syntax to start traversing a singly linked list in C++?

easy

A. Node* current = new Node();

B. Node current = head;

C. Node current = new Node();

D. Node* current = head;

Solution

1. Step 1: Understand pointer usage in linked lists

   In C++, linked list nodes are accessed via pointers, so we use a pointer variable to traverse.

2. Step 2: Identify correct pointer initialization

   We set a pointer 'current' to point to the head node to start traversal: Node* current = head;

3. Final Answer:

   Node* current = head; -> Option D

4. Quick Check:

   Use pointer to start traversal = Node* current = head; [OK]

Hint: Use pointer to traverse linked list starting at head [OK]

Common Mistakes:

• Using object instead of pointer for traversal
• Creating a new node instead of using existing head
• Not initializing traversal pointer correctly

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

struct Node {
  int data;
  Node* next;
};

Node* head = new Node{10, nullptr};
head->next = new Node{20, nullptr};
head->next->next = new Node{30, nullptr};

Node* current = head;
int searchValue = 20;
bool found = false;
while (current != nullptr) {
  if (current->data == searchValue) {
    found = true;
    break;
  }
  current = current->next;
}
if (found) std::cout << "Value found";
else std::cout << "Value not found";

medium

A. Value not found

B. Compilation error

C. Value found

D. Runtime error

Solution

1. Step 1: Trace the linked list nodes and values

   The list has nodes with values 10 -> 20 -> 30. We search for 20.

2. Step 2: Check the search loop logic

   The loop checks each node's data. When it reaches node with 20, found becomes true and loop breaks.

3. Final Answer:

   Value found -> Option C

4. Quick Check:

   20 exists in list, so output = "Value found" [OK]

Hint: Check each node's data until match or end [OK]

Common Mistakes:

• Forgetting to update current pointer
• Using wrong comparison operator
• Not breaking loop after finding value

4. Identify the error in the following code that searches for a value in a linked list:

Node* current = head;
int searchValue = 15;
while (current->next != nullptr) {
  if (current->data == searchValue) {
    std::cout << "Found";
    break;
  }
  current = current->next;
}
if (current == nullptr) std::cout << "Not Found";

medium

A. The loop condition skips checking the last node

B. The searchValue variable is not initialized

C. The current pointer is not updated inside the loop

D. The output statements are missing semicolons

Solution

1. Step 1: Analyze the loop condition

   The loop runs while current->next is not nullptr, so it stops before the last node.

2. Step 2: Understand impact on search

   The last node's data is never checked, so if the value is there, it will be missed.

3. Final Answer:

   The loop condition skips checking the last node -> Option A

4. Quick Check:

   Loop must check all nodes including last [OK]

Hint: Loop on current != nullptr to check all nodes [OK]

Common Mistakes:

• Using current->next != nullptr instead of current != nullptr
• Not checking last node's data
• Incorrectly handling nullptr checks

5. You want to search for a value in a singly linked list and return its position (1-based index). Which approach correctly implements this?

int searchPosition(Node* head, int value) {
  int pos = 1;
  Node* current = head;
  while (current != nullptr) {
    if (current->data == value) return pos;
    current = current->next;
    pos++;
  }
  return -1;
}

hard

A. Returns the position of value or -1 if not found

B. Returns true if value found, false otherwise

C. Returns the last node's data always

D. Returns 0 if value is found at head

Solution

1. Step 1: Understand the function logic

   The function starts position at 1 and traverses nodes, checking data against value.

2. Step 2: Check return values

   If value matches, it returns current position; if not found, returns -1.

3. Final Answer:

   Returns the position of value or -1 if not found -> Option A

4. Quick Check:

   Function returns index or -1 if missing [OK]

Hint: Return index on match, else -1 after full traversal [OK]

Common Mistakes:

• Returning boolean instead of position
• Starting position count at 0 instead of 1
• Not returning -1 when value not found