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Python Linear Search

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Linear Search is the simplest searching algorithm. It goes through each element in a list or array one by one to find the target value.

🔹 When to Use Linear Search?

Use Linear Search when:

  • The list is unsorted

  • Simplicity is preferred over performance

  • The list is small

🔹 Linear Search in Python

def linear_search(arr, target):
    for i in range(len(arr)):
        if arr[i] == target:
            return i
    return -1
Example
numbers = [10, 20, 30, 40, 50]
target = 30

result = linear_search(numbers, target)
print("Found at index:", result)

✅ Output:

Found at index: 2

🔹 What If Element is Not Found?

target = 99
result = linear_search(numbers, target)

if result == -1:
    print("Element not found.")
else:
    print("Found at index:", result)

✅ Output:

Element not found.

🔹 Time Complexity

Case Time
Best Case O(1)
Worst Case O(n)
Average O(n)

Linear Search is not efficient for large datasets.

🔹 Use Cases of Linear Search

  • Searching in an unsorted list

  • Finding the first match

  • Easy to implement without any libraries

Practice Questions

Q1. Write a Python program to search for number 25 in a list of 10 elements using linear search.

Q2. Write a Python program to modify the search function to return True or False instead of the index.

Q3. Write a Python program to perform linear search in a list of strings.

Q4. Write a Python program to handle the case where the target occurs more than once and return all indices.

Q5. Write a Python program to modify the search function to print the number of comparisons made.

Q6. Write a Python program to accept a list and a target value from the user and search for that value.

Q7. Write a Python program to return the last occurrence of the target element in the list.

Q8. Write a Python program to search for a number in a nested list (list of lists).

Q9. Write a Python program to check if a value is present in a list of dictionaries by a specific key.

Q10. Write a Python program to implement linear search without using range() or index values – iterate directly through elements.

Python Linear Search Quiz

Q1: What is Linear Search?

A. Search from middle
B. Search by skipping
C. Search each element one by one
D. Uses binary logic

Q2: What is the best-case time complexity of linear search?

A. O(n)
B. O(log n)
C. O(n^2)
D. O(1)

Q3: What does linear search return if element not found?

A. 0
B. False
C. -1
D. None

Q4: Which data type can you search using linear search?

A. List
B. String
C. Tuple
D. All of the above

Q5: Which one is true about linear search?

A. Only works on sorted lists
B. Needs binary logic
C. Always finds the element
D. Can work on unsorted lists

Q6: In which case is linear search fastest?

A. Element is last
B. Element is middle
C. Element is first
D. Element not found

Q7: How many elements are checked in worst case (length n)?

A. 1
B. n/2
C. n
D. log n

Q8: What is returned on successful match?

A. Element value
B. Index
C. Boolean
D. None

Q9: Is linear search case-sensitive on strings?

A. Yes
B. No
C. Only in Python 2
D. Only if using ASCII encoding

Q10: What does arr[i] == target do?

A. Sorts the array
B. Finds the largest number
C. Compares each element
D. Swaps elements
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