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

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start traversing the linked list from the head node.

DSA C

struct Node* current = [1];

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

Anext

Btail

CNULL

Dhead

Attempts:

3 left

💡 Hint

Common Mistakes

Using tail instead of head to start traversal.

Assigning NULL which means no node.

Using next pointer without a current node.

The traversal of a linked list starts from the head node, so we assign the head pointer to the current pointer.

2fill in blank

medium

Complete the condition to continue traversing until the end of the linked list.

DSA C

while (current [1] NULL) {
    // process current node
    current = current->next;
}

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

A!=

B==

C<

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' which stops immediately if current is not NULL.

Using '<' or '>' which are not valid for pointers.

The loop should continue as long as current is not NULL, meaning there are nodes left to visit.

3fill in blank

hard

Fix the error in the condition to check if the current node's data matches the target value.

DSA C

if (current->data [1] target) {
    return 1; // found
}

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

A<=

B==

C!=

D=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '=' instead of '==' causes assignment, not comparison.

Using '!=' checks for inequality, which is wrong here.

Use '==' to compare values for equality in C. '=' is assignment, which is incorrect here.

4fill in blank

hard

Fill both blanks to complete the search function that returns 1 if found, 0 otherwise.

DSA C

struct Node* current = head;
while (current [1] NULL) {
    if (current->data [2] target) {
        return 1;
    }
    current = current->next;
}
return 0;

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

A!=

B==

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' in the loop condition which stops immediately.

Using '!=' in the if condition which checks for inequality.

The loop continues while current is not NULL, and inside the loop, we check if current->data equals the target.

5fill in blank

hard

Fill all three blanks to create a function that searches for a value in a linked list and returns 1 if found, else 0.

DSA C

int search(struct Node* head, int target) {
    struct Node* current = [1];
    while (current [2] NULL) {
        if (current->data [3] target) {
            return 1;
        }
        current = current->next;
    }
    return 0;
}

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

Ahead

B!=

C==

DNULL

Attempts:

3 left

💡 Hint

Common Mistakes

Starting from NULL instead of head.

Using '=' instead of '==' for comparison.

Loop condition using '==' instead of '!='.

The function starts from head, loops while current is not NULL, and checks if current->data equals the target.

Practice

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

easy

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

B. To add a new node at the end of 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 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 linked list.

3. Final Answer:

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

4. Quick Check:

   Search = Find value in list [OK]

Hint: Search means look for a value in nodes [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 way to start searching a linked list in C?

easy

A. Node* current = head; while(current != NULL) { if(current->data == value) break; current = current->next; }

B. Node* current = NULL; while(current != head) { if(current->data == value) break; current = current->next; }

C. Node* current = head; while(current->next != NULL) { if(current->data == value) break; current = current->next; }

D. Node* current = head; for(int i=0; inext; }

Solution

1. Step 1: Initialize pointer to head

   We start searching from the head node, so current = head is correct.

2. Step 2: Traverse until end or value found

   Loop continues while current is not NULL, checking each node's data.

3. Final Answer:

   Node* current = head; while(current != NULL) { if(current->data == value) break; current = current->next; } -> Option A

4. Quick Check:

   Start at head and loop till NULL [OK]

Hint: Start at head, loop until NULL or value found [OK]

Common Mistakes:

• Initializing current to NULL instead of head
• Looping until current->next is NULL misses last node
• Using for loop with value as count incorrectly

3. What will be the output of the following code snippet if the linked list contains nodes with values 3 -> 7 -> 10 -> NULL and we search for 7?

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

int search(Node* head, int value) {
  Node* current = head;
  while(current != NULL) {
    if(current->data == value) {
      return 1;
    }
    current = current->next;
  }
  return 0;
}

int main() {
  Node n3 = {10, NULL};
  Node n2 = {7, &n3};
  Node n1 = {3, &n2};
  int found = search(&n1, 7);
  printf("%d", found);
  return 0;
}

medium

A. Compilation error

B. 0

C. 7

D. 1

Solution

1. Step 1: Trace the search function

   The function checks each node's data: 3 (no), 7 (yes), so it returns 1 immediately.

2. Step 2: Understand main output

   Main prints the returned value, which is 1, indicating value found.

3. Final Answer:

   1 -> Option D

4. Quick Check:

   Value found = 1 [OK]

Hint: Returns 1 if found, else 0 [OK]

Common Mistakes:

• Expecting the value itself to be printed
• Confusing return 1 with return 0
• Thinking code causes compilation error

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

int search(Node* head, int value) {
  Node* current = head;
  while(current->next != NULL) {
    if(current->data == value) {
      return 1;
    }
    current = current->next;
  }
  return 0;
}

medium

A. The function returns 1 even if value is not found

B. The pointer current is not initialized

C. The loop condition misses checking the last node

D. The function should return the node pointer instead of int

Solution

1. Step 1: Analyze loop condition

   The loop runs while current->next != NULL, so it stops before last node.

2. Step 2: Consequence of condition

   The last node's data is never checked, so search may miss value at last node.

3. Final Answer:

   The loop condition misses checking the last node -> Option C

4. Quick Check:

   Loop condition excludes last node [OK]

Hint: Loop until current != NULL to check all nodes [OK]

Common Mistakes:

• Using current->next != NULL instead of current != NULL
• Assuming last node is checked automatically
• Confusing return types

5. Given a linked list with nodes containing values 5 -> 8 -> 12 -> 20 -> NULL, write a function to search for a value and return the position (1-based) if found, or -1 if not found. What will be the output when searching for 12?

hard

A. -1

B. 3

C. 2

D. 4

Solution

1. Step 1: Understand position counting

   Positions start at 1 for head node, increment by 1 for each next node.

2. Step 2: Locate value 12 in list

   Values: 5 (pos 1), 8 (pos 2), 12 (pos 3), so 12 is at position 3.

3. Final Answer:

   3 -> Option B

4. Quick Check:

   Value 12 is third node [OK]

Hint: Count nodes from head until value found [OK]

Common Mistakes:

• Returning zero-based index instead of 1-based
• Returning -1 even if value exists
• Confusing position with value