Linear Search Algorithm in DSA C++ - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of Linear Search on Array

What is the output of the following C++ code that performs a linear search for the value 7 in the array?

DSA C++

int arr[] = {3, 5, 7, 9, 11};
int n = 5;
int target = 7;
int index = -1;
for (int i = 0; i < n; i++) {
    if (arr[i] == target) {
        index = i;
        break;
    }
}
std::cout << index << std::endl;

A -1

B 2

C 3

D 0

💡 Hint

Remember that array indexing in C++ starts at 0.

The value 7 is at index 2 in the array. The loop stops when it finds 7 and prints 2.

❓ Predict Output

intermediate

Linear Search Result When Target Not Found

What will be the output of this C++ code when searching for 10 in the array?

DSA C++

int arr[] = {1, 2, 3, 4, 5};
int n = 5;
int target = 10;
int index = -1;
for (int i = 0; i < n; i++) {
    if (arr[i] == target) {
        index = i;
        break;
    }
}
std::cout << index << std::endl;

A -1

B 4

C 0

D 5

💡 Hint

If the target is not found, the index remains -1.

Since 10 is not in the array, the loop never updates index from -1, so -1 is printed.

🔧 Debug

advanced

Find the Bug in Linear Search Implementation

This code is supposed to perform a linear search but does not work correctly. What is the output and why?

DSA C++

int arr[] = {2, 4, 6, 8};
int n = 4;
int target = 10;
int index = -1;
for (int i = 1; i <= n; i++) {
    if (arr[i] == target) {
        index = i;
        break;
    }
}
std::cout << index << std::endl;

A 2

B -1

C 3

D Runtime error

💡 Hint

Check the loop boundaries and array indexing carefully.

The loop accesses arr[4] when i == 4, which is out of bounds causing undefined behavior or runtime error.

🧠 Conceptual

advanced

Time Complexity of Linear Search

What is the worst-case time complexity of linear search on an array of size n?

A O(n)

B O(log n)

C O(n log n)

D O(1)

💡 Hint

Consider how many elements you might check if the target is not present.

In the worst case, linear search checks every element once, so it takes O(n) time.

🚀 Application

expert

Linear Search on Linked List

Given a singly linked list with nodes containing values [10, 20, 30, 40], what is the output of searching for 30 using linear search?

DSA C++

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};
head->next->next->next = new Node{40, nullptr};

int target = 30;
int index = 0;
Node* current = head;
while (current != nullptr) {
    if (current->data == target) {
        break;
    }
    current = current->next;
    index++;
}
if (current == nullptr) index = -1;
std::cout << index << std::endl;

A 1

B 3

C 2

D -1

💡 Hint

Count nodes starting from 0 until you find the target value.

The value 30 is in the third node, which is index 2 starting from 0.