Search for a Value in Linked List in DSA C

Mental Model

We look at each item in the list one by one until we find the value or reach the end.

Analogy: Like flipping through pages of a book to find a specific word, checking each page in order.

head -> [1] -> [2] -> [3] -> null

Dry Run Walkthrough

Input: list: 1 -> 2 -> 3, search for value 2

Goal: Find if the value 2 exists in the list and where

Step 1: Start at the first node with value 1

head -> [1 ↑] -> [2] -> [3] -> null

Why: We begin searching from the start of the list

Step 2: Check if current node value 1 equals 2 (it does not), move to next node

head -> [1] -> [2 ↑] -> [3] -> null

Why: Value not found yet, so we continue to next node

Step 3: Check if current node value 2 equals 2 (it does), stop search

head -> [1] -> [2 ↑] -> [3] -> null

Why: Found the value we are searching for

Result:

head -> [1] -> [2 ↑] -> [3] -> null
Value 2 found in the list

Annotated Code

DSA C

#include <stdio.h>
#include <stdlib.h>

// Node structure for linked list
typedef struct Node {
    int data;
    struct Node* next;
} Node;

// Function to create a new node
Node* create_node(int value) {
    Node* new_node = (Node*)malloc(sizeof(Node));
    new_node->data = value;
    new_node->next = NULL;
    return new_node;
}

// Function to search for a value in the linked list
int search_value(Node* head, int target) {
    Node* current = head; // start at head
    while (current != NULL) { // while not end of list
        if (current->data == target) {
            return 1; // found the value
        }
        current = current->next; // move to next node
    }
    return 0; // value not found
}

// Function to print the linked list
void print_list(Node* head, int highlight) {
    Node* current = head;
    while (current != NULL) {
        if (current->data == highlight) {
            printf("[%d ↑] -> ", current->data); // highlight found node
        } else {
            printf("[%d] -> ", current->data);
        }
        current = current->next;
    }
    printf("null\n");
}

int main() {
    // Create linked list 1 -> 2 -> 3 -> null
    Node* head = create_node(1);
    head->next = create_node(2);
    head->next->next = create_node(3);

    int target = 2;
    int found = search_value(head, target);

    print_list(head, found ? target : -1);
    if (found) {
        printf("Value %d found in the list\n", target);
    } else {
        printf("Value %d not found in the list\n", target);
    }

    // Free memory
    Node* current = head;
    while (current != NULL) {
        Node* temp = current;
        current = current->next;
        free(temp);
    }

    return 0;
}

Node* current = head; // start at head

initialize current pointer to start of list

while (current != NULL) { // while not end of list

loop through nodes until end

if (current->data == target) {

check if current node has target value

return 1; // found the value

stop search and report found

current = current->next; // move to next node

advance to next node to continue search

Output

[1] -> [2 ↑] -> [3] -> null

Value 2 found in the list

Complexity Analysis

Time: O(n) because in worst case we check each node once until we find the value or reach the end

Space: O(1) because we only use a few variables regardless of list size

vs Alternative: Compared to arrays, linked list search is similar O(n), but linked lists do not allow direct access so traversal is necessary

Edge Cases

Empty list (head is NULL)

Search immediately returns not found

DSA C

while (current != NULL) {

Value not in list

Search traverses entire list and returns not found

DSA C

while (current != NULL) {

Value at head node

Search finds value immediately and returns found

DSA C

if (current->data == target) {

When to Use This Pattern

When you need to find if a value exists in a linked list, use linear search by checking each node one by one.

Common Mistakes

Mistake: Not checking if current node is NULL before accessing data
Fix: Always check current != NULL in the loop condition before accessing current->data

Summary

Searches through a linked list to find if a value exists.

Use when you need to check presence of a value in a linked list.

The key is to check each node one by one until you find the value or reach the end.