Post date: Oct 28, 2024, 06:22 PM

Read time: 15 min

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Post date: Oct 28, 2024, 06:22 PM

Read time: 15 min

Type:

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DALL·E 2024-10-29 00 20 33 - A modern thumbnail for a blog post on common software development interview topics in Bangladesh, 2024 The image should feature a clean, professional

Common Topics for Software Development Interviews and Written Tests in Bangladesh, 2024

I recently applied for some entry-level or mid-level software development positions in October 2024 and had several interviews. In my experience, they usually begin by asking questions on fundamental CSE topics. These topics are also commonly covered in the written exams and include questions relevant to the job post.

For write code on pen and paper without an IDE

1. Prime Number Check

python

1def is_prime(n):
2  if n <= 1:
3    return False
4  for i in range(2, int(n ** 0.5) + 1):
5    if n % i == 0:
6      return False
7  return True
8
9
10print(is_prime(17)) # Output: True

2. Leap Year Calculation

python

1def is_leap(year):
2  return (year % 4 == 0 and year % 100 != 0) or (year % 400 == 0)
3
4print(is_leap(2024)) # Output: True

3. Fibonacci Sequence

python

1def fibonacci(n):
2    feb_seq = [0, 1]
3    while len(feb_seq) < n:
4        feb_seq.append(feb_seq[-2] + feb_seq[-1])
5    return feb_seq[:n]
6
7print(fibonacci(5)) # Output: [0, 1, 1, 2, 3]

4. Factorial Calculator

python

1def factorial(n):
2    if n == 0 or n == 1:
3        return 1
4    return n * factorial(n - 1)
5
6print(factorial(5)) # Output: 120

5. Palindrome Checker

python

1def is_palindrom(s):
2    return s == s[::-1]
3
4print(is_palindrom('madam')) # Output: True
5print(is_palindrom('cat')) # Output: False

6. Armstrong number

python

1def is_armstrong(n):
2    digits = list(map(int, str(n)))
3    power = len(digits)
4    return n == sum([digit ** power for digit in digits])
5
6print(is_armstrong(153)) # Output: True

7. Greatest Common Divisor (GCD)

python

1def gcd(a, b):
2    while b:
3        a, b = b, a % b
4    return a
5
6print(gcd(60, 48)) # Output: 12

8. Sum of Digits

python

1def sum_of_digits(n):
2    return sum(map(int, str(n)))
3
4print(sum_of_digits(12345)) # Output: 15

9. Reverse a String

python

1def reverse_string(s):
2    return s[::-1]
3
4print(reverse_string('madam')) # Output: madam

10. Bubble Sort

python

1def bubble_sort(arr):
2    n = len(arr)
3    for i in range(n):
4        for j in range(0, n-i-1):
5            if arr[j] > arr[j+1]:
6                arr[j], arr[j+1] = arr[j+1], arr[j]
7    return arr
8
9print(bubble_sort([0, 10, 11, 1, 2])) # Output: [0, 1, 2, 10, 11]

11. Binary Search

python

1def binary_search(arr, target):
2    low, high = 0, len(arr) - 1
3   
4    while low <= high:
5        mid = (low + high) //2
6        if arr[mid] == target:
7            return mid
8        elif arr[mid] < target:
9            low = mid + 1
10        else:
11            high = mid - 1
12    return -1
13
14arr = [1, 2, 4, 5, 7, 9, 0, 10]
15target = 7
16
17print(binary_search(arr, target))

12. Find Max value in array

python

1def find_max(arr):
2    max_val = arr[0]
3    for num in arr[1:]:
4        if num > max_val:
5            max_val = num
6    return max_val
7
8print(find_max([1, 2, 4, 10, 11, 0])) # Output: 11

13. Write a Python function to find the second largest number in a list.

python

1def second_largest(numbers):
2    if len(numbers) < 2:
3        return None
4    unique_sorted = sorted(set(numbers), reverse=True)
5    return unique_sorted[1] if len(unique_sorted) > 1 else None
6
7# Example usage
8print(second_largest([10, 5, 8, 12, 3, 12, 7]))  # Output: 10
9print(second_largest([1, 1, 1]))  # Output: None

14. Remove duplicate in array

python

1arr = [1, 2, 2, 3, 4, 4, 5]
2arr = list(set(arr))
3print(arr) # Output might be in a different order

14.1 Using List Comprehension with enumerate

python

1arr = [1, 2, 2, 3, 4, 4, 5]
2unique_arr = [item for index, item in enumerate(arr) if item not in arr[:index]]
3print(unique_arr)  # Output: [1, 2, 3, 4, 5]

15. Swap value using a temporary variable

python

1a = 5
2b = 10
3temp = a
4a = b
5b = temp
6print(a)  # Output: 10
7print(b)  # Output: 5

OOP

Object-oriented programming (OOP) is a computer programming model that organises software design around data, or objects, rather than functions and logic. An object can be defined as a data field that has unique attributes and behaviour.

Object-oriented programming (OOP) has four pillars of concept:

Encapsulation
Abstraction
Inheritance
Polymorphism - Overloading and Overriding

1. Encapsulation

Encapsulation is the concept of bunding data (attributes) and methods(functions) that work on the data into a single unit, usually in the form of a class. It restricts direct access to certain components and ensures control over how data is accessed and modified. Key point: Private attributes (denoted by an double underscore in __ python), access or modify the private attributes via getter and setter methods.

Example

python

1class Person:
2    def __init__(self, name, age):
3        self.__name = name  # Private variable
4        self.__age = age    # Private variable
5
6
7    # Getter method for name
8    def get_name(self):
9        return self.__name
10
11
12    # Setter method for name
13    def set_name(self, name):
14        self.__name = name
15
16
17    # Getter method for age
18    def get_age(self):
19        return self.__age
20
21
22    # Setter method for age
23    def set_age(self, age):
24        if age > 0:
25            self.__age = age
26        else:
27            print("Age cannot be negative.")
28
29
30# Usage
31person = Person("Alice", 25)
32print(person.get_name())  # Output: Alice
33person.set_age(30)
34print(person.get_age())   # Output: 30

2. Abstraction

Abstraction focuses on exposing only the necessary details while hiding the complexities. It is achieved using abstract classes or interfaces.

Key point: Abstract class contains one or more abstract methods (Methods without implementation). These abstract methods must be implemented by any concrete class ( a non-abstract class) that inherits from the abstract class.

Example

python

1from abc import ABC, abstractmethod
2
3
4# Abstract class
5class Shape(ABC):
6    @abstractmethod
7    def area(self):
8        pass
9
10
11# Concrete class
12class Circle(Shape):
13    def __init__(self, radius):
14        self.radius = radius
15
16
17    # Implementing the abstract method
18    def area(self):
19        return 3.14 * self.radius * self.radius
20
21
22# Concrete class
23class Rectangle(Shape):
24    def __init__(self, width, height):
25        self.width = width
26        self.height = height
27
28
29    # Implementing the abstract method
30    def area(self):
31        return self.width * self.height
32
33
34# Usage
35circle = Circle(5)
36rectangle = Rectangle(4, 6)
37
38
39print("Circle area:", circle.area())  # Output: Circle area: 78.5
40print("Rectangle area:", rectangle.area())  # Output: Rectangle area: 24

3. Inheritance

Inheritance allows one class to inherit properties and methods from another class. This promotes code reuse and a hierarchical class structure.

Key point: Base class(parent class), the class whose properties and methods are inherited. Derived class(child class), the class that inherits properties and methods from the base class.

Example

python

1# Base class
2class Animal:
3    def __init__(self, name):
4        self.name = name
5
6
7    def make_sound(self):
8        print(f"{self.name} makes a sound")
9
10
11# Derived class
12class Dog(Animal):
13    def __init__(self, name, breed):
14        super().__init__(name)  # Call the constructor of the base class
15        self.breed = breed
16
17
18    # Override the method
19    def make_sound(self):
20        print(f"{self.name} barks!")
21
22
23# Derived class
24class Cat(Animal):
25    def make_sound(self):
26        print(f"{self.name} meows!")
27
28
29# Usage
30dog = Dog("Buddy", "Golden Retriever")
31cat = Cat("Whiskers")
32
33
34dog.make_sound()  # Output: Buddy barks!
35cat.make_sound()  # Output: Whiskers meows!

4. Polymorphism

Polymorphism allows objects of different classes to be treated as objects of a common super class. It enables the same method to perform different behaviours based on the object calling it.

Key point: Method Overriding: Redefining a method in a derived class that exist in the base class. Method Overloading: Having multiple methods with the same name but different parameters (not supported natively in Python, but can be mimicked using default arguments or other techniques).

Example of Method Overloading

python

1class Calculator:
2    def add(self, a, b, c=None):
3        if c is not None:
4            return a + b + c
5        else:
6            return a + b
7
8
9calc = Calculator()
10print(calc.add(1, 2))      # 3
11print(calc.add(1, 2, 3))   # 6

Example of Method Overriding

python

1class Animal:
2    def speak(self):
3        return "Animal makes a sound"
4
5
6class Dog(Animal):
7    def speak(self):
8        return "Dog barks"
9
10
11dog = Dog()
12print(dog.speak())  # Outputs: Dog barks

BankAccount Class

python

1class BankAccount:
2    def __init__(self, balance=0):
3        self.balance = balance
4   
5    def deposit(self, amount):
6        if amount > 0:
7            self.balance += amount
8        else:
9            raise ValueError("Deposit amount must be positive.")
10   
11    def withdraw(self, amount):
12        if amount > self.balance:
13            raise ValueError("Insufficient funds.")
14        self.balance -= amount
15   
16    def check_balance(self):
17        return self.balance

Shallow vs deep copy

Shallow copy: Copies the reference to object not the objects themselves
Deep copy: Copies the object and all nested objects, creating independent duplicates

python

1import copy
2
3list1 = [[1, 2], [3, 4]]
4shallow_copy = copy.copy(list1)
5deep_copy = copy.deepcopy(list1)
6
7list1[0][0] = 99  # Affects shallow_copy but not deep_copy

Data Structures and Algorithms

Stack

A stack is a linear data structure that follows the LIFO (Last in, First Out) principle. The last element added to the stack in the first one to be removed.

Common Operations:

Push: Add an element to the top of the stack.
Pop: Remove and return the top element from the stack.
Peek: View the top element without removing it.

Real-world example:

Think of a stack of plates. The last plate you put on the top is the first one you take off.
Usages: Undo functionality in software like text editors or drawing programs

Queue

A queue is a linear data structure that follows the FIFO(First in, First Out) principle. The first element added to the queue is the first one to be removed.

Common operations:

Enqueue: Add an element to the end of the queue
Dequeue: Remove an element to the first.

Real-world example:

Think of a line at a bank counter. The first person in line gets served first.
Usages: Printer queue (Jobs are prints in the order they arrive) or handling requests in a web server.

Example Stack and Queue

python

1class Stack:
2    def __init__(self):
3        self.items = []
4
5    def push(self, item):
6        self.items.append(item)
7
8    def pop(self):
9        return self.items.pop() if not self.is_empty() else None
10
11    def is_empty(self):
12        return len(self.items) == 0
13
14class Queue:
15    def __init__(self):
16        self.items = []
17
18    def enqueue(self, item):
19        self.items.insert(0, item)
20
21    def dequeue(self):
22        return self.items.pop() if not self.is_empty() else None
23
24    def is_empty(self):
25        return len(self.items) == 0
26
27# Example usage
28stack = Stack()
29stack.push(1)
30stack.push(2)
31print(stack.pop())  # Output: 2
32
33queue = Queue()
34queue.enqueue('a')
35queue.enqueue('b')
36print(queue.dequeue())  # Output: 'a'

Reverse a Linked List

Linked List Overview: A linked list is a data structure in which each element (node) contains a data part and a reference (or pointer) to the next node in the sequence. Linked lists are useful for dynamic data storage where the size can change over time.

Types

Singly Linked list: Each node points to the next node.
Doubly Linked list: Each node has pointers to both the next and previous nodes.

Implementing a Singly Linked List

python

1class Node:
2    def __init__(self, data):
3        self.data = data
4        self.next = None
5
6class SinglyLinkedList:
7    def __init__(self):
8        self.head = None
9
10    def insert(self, data):
11        new_node = Node(data)
12        if not self.head:
13            self.head = new_node
14        else:
15            current = self.head
16            while current.next:
17                current = current.next
18            current.next = new_node
19
20    def display(self):
21        current = self.head
22        while current:
23            print(current.data, end=" -> ")
24            current = current.next
25        print("None")
26
27# Example usage
28sll = SinglyLinkedList()
29sll.insert(1)
30sll.insert(2)
31sll.insert(3)
32sll.display()  # Output: 1 -> 2 -> 3 -> None

Reversing a Singly Linked list

To reverse a linked list, we need to iterate through the list and reverse the next pointers of the nodes so that they point to the previous node.

Example

python

1# Define a Node class
2class Node:
3    def __init__(self, data):
4        self.data = data
5        self.next = None
6
7
8# Function to reverse a linked list
9def reverse_linked_list(head):
10    prev = None
11    current = head
12   
13    # Iterate through the list
14    while current:
15        next_node = current.next  # Store the next node
16        current.next = prev       # Reverse the 'next' pointer
17        prev = current            # Move prev to current node
18        current = next_node       # Move to the next node
19   
20    # After the loop, prev will be the new head
21    return prev
22
23
24# Helper function to print a linked list
25def print_linked_list(head):
26    current = head
27    while current:
28        print(current.data, end=" -> ")
29        current = current.next
30    print("None")
31
32
33# Example Usage
34# Creating a linked list: 1 -> 2 -> 3 -> 4 -> None
35head = Node(1)
36head.next = Node(2)
37head.next.next = Node(3)
38head.next.next.next = Node(4)
39
40
41print("Original Linked List:")
42print_linked_list(head)
43
44
45# Reversing the linked list
46new_head = reverse_linked_list(head)
47
48
49print("Reversed Linked List:")
50print_linked_list(new_head)

Complexity

Time Complexity: O(n) where n is the number of nodes in the linked list (we visit each node once)
Space Complexity: O(1), because we only use a few extra pointers.

Quicksort Algorithm and Time Complexity

Quicksort is a divide-and-conquer sorting algorithm that selects a “pivot” element and partitions the array into two sub-arrays: One with elements less than the pivot and the other with elements greater than the pivot. The process is recursively applied to both sub-arrays.

Steps

Pick a pivot: select a pivot element from the array(commonly the first, last or middle element or a random one)
Partitioning: Rearrange the array such that all elements less than the pivot are on the left side and all elements greater than the pivot are on the right side.
Recursion: Recursively apply the same process to the left and right sub-arrays
Base case: Stop when the sub-arrays contain only one element (already sorted).

Example

python

1def quicksort(arr):
2    # Base case: array is empty or has one element
3    if len(arr) <= 1:
4        return arr
5    else:
6        pivot = arr[len(arr) // 2]  # Choose the middle element as the pivot
7        left = [x for x in arr if x < pivot]   # All elements less than pivot
8        middle = [x for x in arr if x == pivot]  # All elements equal to pivot
9        right = [x for x in arr if x > pivot]  # All elements greater than pivot
10       
11        # Recursively apply quicksort to left and right sub-arrays
12        return quicksort(left) + middle + quicksort(right)
13
14# Example usage
15arr = [3, 6, 8, 10, 1, 2, 1]
16sorted_arr = quicksort(arr)
17print("Sorted Array:", sorted_arr)

Complexity

Time

Base case: O(n log n) occurs when the pivot consistently divides the array into balanced sub-arrays
Average case: O(n log n) as the array is usually split in a relatively balanced manner.
Worst case: O(n^2) occurs when the pivot divides the array into very unbalanced sub-arrays
Worst case example:
If the array is already sorted, and we always pick the first or last element as the pivot, we repeatedly partition the array into one large sub-array and one empty one, leading to O(n^2) behaviour.

Space

O(log n) Due to the recursion stack in the best and average cases.
O(n) in the worst case because of the recursion depth when the pivot leads to highly unbalanced partitions.

CRUD operations in SQL

CRUD operations in SQL refer to the basic operations we can perform on a database: Create, Read, Update, and Delete.

1. Create (INSEART)

sql

1CREATE TABLE Employees (
2    EmployeeID INT PRIMARY KEY,
3    FirstName VARCHAR(50),
4    LastName VARCHAR(50),
5    Salary DECIMAL(10, 2)
6);
7
8INSERT INTO Employees (EmployeeID, FirstName, LastName, Salary)
9VALUES (1, 'John', 'Doe', 50000.00);

2. Read (SELECT)

sql

1SELECT FirstName, LastName, Salary
2FROM Employees
3WHERE Salary > 40000;

3. Update(UPDATE)

sql

1UPDATE Employees
2SET Salary = 55000
3WHERE EmployeeID = 1;

4. Delete (DELETE)

sql

1DELETE FROM Employees
2WHERE EmployeeID = 1;

SQL Basics

JOIN

There are different types of joins, but the most common is the INNER JOIN, which returns only matching rows between two tables.

sql

1-- Table: Orders
2OrderID | CustomerID | OrderDate
3--------------------------------
41       | 1          | 2024-01-01
52       | 2          | 2024-02-01
6
7
8-- Table: Customers
9CustomerID | Name       | City
10------------------------------
111          | John Smith | New York
122          | Jane Doe   | Los Angeles
13
14
15-- INNER JOIN Example
16SELECT Orders.OrderID, Customers.Name, Orders.OrderDate
17FROM Orders
18INNER JOIN Customers ON Orders.CustomerID = Customers.CustomerID;
19
20
21-- Result
22OrderID | Name       | OrderDate
23--------------------------------
241       | John Smith | 2024-01-01
252       | Jane Doe   | 2024-02-01

GROUP BY and HAVING

Group by is used to group records with the same values.
Having is used to filter records after Group by is applied

sql

1SELECT City, COUNT(CustomerID) AS NumberOfCustomers
2FROM Customers
3GROUP BY City
4HAVING COUNT(CustomerID) > 1;

Aggregate Functions

sql

1-- Count the number of employees
2SELECT COUNT(*) AS TotalEmployees
3FROM Employees;
4
5
6-- Find the maximum salary
7SELECT MAX(Salary) AS HighestSalary
8FROM Employees;
9
10
11-- Find the average salary
12SELECT AVG(Salary) AS AverageSalary
13FROM Employees;
14
15
16-- Find the total salary cost
17SELECT SUM(Salary) AS TotalSalaryCost
18FROM Employees;

ACID Properties

ACID is an acronym that stands for Atomicity, Consistency, Isolation, and Durability. These are key properties of database transactions to ensure data integrity.

ACID Explained:

Atomicity: Ensures that all operations within a transaction are completed successfully, or none of them are. If one part of a transaction fails, the entire transaction is rolled back.
- Example: Transferring money from one bank account to another – either both accounts are updated, or none are.
Consistency: Ensures that a transaction brings the database from one valid state to another, maintaining all predefined rules (such as constraints, triggers).
- Example: If a field is marked as NOT NULL, no transaction should allow inserting a NULL value.
Isolation: Ensures that concurrent execution of transactions leads to the same state as if the transactions were executed sequentially.
- Example: If two users try to book the last seat in a cinema simultaneously, only one transaction should succeed.
Durability: Once a transaction has been committed, it remains so, even in the case of a system failure (e.g., power outage).
- Example: After transferring money, the updated balances should remain persistent even if the system crashes.

Basic AI Knowledge

Question: Explain the difference between supervised and unsupervised learning in machine learning.

Supervised Learning:

Uses labeled data
The algorithm learns to predict outputs based on input features
Examples: classification, regression
Use case: spam detection, price prediction

Unsupervised Learning:

Uses unlabeled data
The algorithm finds patterns or structures in the data
Examples: clustering, dimensionality reduction
Use case: customer segmentation, anomaly detection
Python example of supervised learning (Linear Regression):

python

1from sklearn.linear_model import LinearRegression
2import numpy as np
3
4# Sample data
5X = np.array([[1], [2], [3], [4], [5]])
6y = np.array([2, 4, 5, 4, 5])
7
8# Create and train the model
9model = LinearRegression()
10model.fit(X, y)
11
12# Make a prediction
13print(model.predict([[6]]))  # Predict for X = 6

Analytical Skills

Question: Given a scenario: "A city wants to optimize its traffic light system to reduce congestion." Describe your approach to analyzing this problem and proposing a solution.

Approach:

Data Collection:

Traffic flow patterns
Peak hours and congestion points
Current traffic light timings

Analysis:

Identify bottlenecks and high-congestion areas
Analyze the relationship between light timings and traffic flow

Propose Solution:

Implement an AI-based adaptive traffic control system
Use real-time data from sensors and cameras
Dynamically adjust light timings based on current traffic conditions

Implementation:

Start with a pilot program in high-congestion areas
Use machine learning algorithms to continuously improve the system

Evaluation:

Compare traffic flow before and after implementation
Measure reduction in average wait times and overall congestion

These may not be enough, but they cover 70-80% of frequently asked topics. Start with these related topics. If you plan on applying, learn more about these areas.

Thank you very much for reading my blog. 🙌

DALL·E 2024-10-29 00 20 33 - A modern thumbnail for a blog post on common software development interview topics in Bangladesh, 2024 The image should feature a clean, professional

Common Topics for Software Development Interviews and Written Tests in Bangladesh, 2024

For write code on pen and paper without an IDE

1. Prime Number Check

python

1def is_prime(n):
2  if n <= 1:
3    return False
4  for i in range(2, int(n ** 0.5) + 1):
5    if n % i == 0:
6      return False
7  return True
8
9
10print(is_prime(17)) # Output: True

2. Leap Year Calculation

python

1def is_leap(year):
2  return (year % 4 == 0 and year % 100 != 0) or (year % 400 == 0)
3
4print(is_leap(2024)) # Output: True

3. Fibonacci Sequence

python

1def fibonacci(n):
2    feb_seq = [0, 1]
3    while len(feb_seq) < n:
4        feb_seq.append(feb_seq[-2] + feb_seq[-1])
5    return feb_seq[:n]
6
7print(fibonacci(5)) # Output: [0, 1, 1, 2, 3]

4. Factorial Calculator

python

1def factorial(n):
2    if n == 0 or n == 1:
3        return 1
4    return n * factorial(n - 1)
5
6print(factorial(5)) # Output: 120

5. Palindrome Checker

python

1def is_palindrom(s):
2    return s == s[::-1]
3
4print(is_palindrom('madam')) # Output: True
5print(is_palindrom('cat')) # Output: False

6. Armstrong number

python

1def is_armstrong(n):
2    digits = list(map(int, str(n)))
3    power = len(digits)
4    return n == sum([digit ** power for digit in digits])
5
6print(is_armstrong(153)) # Output: True

7. Greatest Common Divisor (GCD)

python

1def gcd(a, b):
2    while b:
3        a, b = b, a % b
4    return a
5
6print(gcd(60, 48)) # Output: 12

8. Sum of Digits

python

1def sum_of_digits(n):
2    return sum(map(int, str(n)))
3
4print(sum_of_digits(12345)) # Output: 15

9. Reverse a String

python

1def reverse_string(s):
2    return s[::-1]
3
4print(reverse_string('madam')) # Output: madam

10. Bubble Sort

python

1def bubble_sort(arr):
2    n = len(arr)
3    for i in range(n):
4        for j in range(0, n-i-1):
5            if arr[j] > arr[j+1]:
6                arr[j], arr[j+1] = arr[j+1], arr[j]
7    return arr
8
9print(bubble_sort([0, 10, 11, 1, 2])) # Output: [0, 1, 2, 10, 11]

11. Binary Search

python

1def binary_search(arr, target):
2    low, high = 0, len(arr) - 1
3   
4    while low <= high:
5        mid = (low + high) //2
6        if arr[mid] == target:
7            return mid
8        elif arr[mid] < target:
9            low = mid + 1
10        else:
11            high = mid - 1
12    return -1
13
14arr = [1, 2, 4, 5, 7, 9, 0, 10]
15target = 7
16
17print(binary_search(arr, target))

12. Find Max value in array

python

1def find_max(arr):
2    max_val = arr[0]
3    for num in arr[1:]:
4        if num > max_val:
5            max_val = num
6    return max_val
7
8print(find_max([1, 2, 4, 10, 11, 0])) # Output: 11

13. Write a Python function to find the second largest number in a list.

python

1def second_largest(numbers):
2    if len(numbers) < 2:
3        return None
4    unique_sorted = sorted(set(numbers), reverse=True)
5    return unique_sorted[1] if len(unique_sorted) > 1 else None
6
7# Example usage
8print(second_largest([10, 5, 8, 12, 3, 12, 7]))  # Output: 10
9print(second_largest([1, 1, 1]))  # Output: None

14. Remove duplicate in array

python

1arr = [1, 2, 2, 3, 4, 4, 5]
2arr = list(set(arr))
3print(arr) # Output might be in a different order

14.1 Using List Comprehension with enumerate

python

1arr = [1, 2, 2, 3, 4, 4, 5]
2unique_arr = [item for index, item in enumerate(arr) if item not in arr[:index]]
3print(unique_arr)  # Output: [1, 2, 3, 4, 5]

15. Swap value using a temporary variable

python

1a = 5
2b = 10
3temp = a
4a = b
5b = temp
6print(a)  # Output: 10
7print(b)  # Output: 5

OOP

Object-oriented programming (OOP) has four pillars of concept:

Encapsulation
Abstraction
Inheritance
Polymorphism - Overloading and Overriding

1. Encapsulation

Example

python

1class Person:
2    def __init__(self, name, age):
3        self.__name = name  # Private variable
4        self.__age = age    # Private variable
5
6
7    # Getter method for name
8    def get_name(self):
9        return self.__name
10
11
12    # Setter method for name
13    def set_name(self, name):
14        self.__name = name
15
16
17    # Getter method for age
18    def get_age(self):
19        return self.__age
20
21
22    # Setter method for age
23    def set_age(self, age):
24        if age > 0:
25            self.__age = age
26        else:
27            print("Age cannot be negative.")
28
29
30# Usage
31person = Person("Alice", 25)
32print(person.get_name())  # Output: Alice
33person.set_age(30)
34print(person.get_age())   # Output: 30

2. Abstraction

Abstraction focuses on exposing only the necessary details while hiding the complexities. It is achieved using abstract classes or interfaces.

Example

python

1from abc import ABC, abstractmethod
2
3
4# Abstract class
5class Shape(ABC):
6    @abstractmethod
7    def area(self):
8        pass
9
10
11# Concrete class
12class Circle(Shape):
13    def __init__(self, radius):
14        self.radius = radius
15
16
17    # Implementing the abstract method
18    def area(self):
19        return 3.14 * self.radius * self.radius
20
21
22# Concrete class
23class Rectangle(Shape):
24    def __init__(self, width, height):
25        self.width = width
26        self.height = height
27
28
29    # Implementing the abstract method
30    def area(self):
31        return self.width * self.height
32
33
34# Usage
35circle = Circle(5)
36rectangle = Rectangle(4, 6)
37
38
39print("Circle area:", circle.area())  # Output: Circle area: 78.5
40print("Rectangle area:", rectangle.area())  # Output: Rectangle area: 24

3. Inheritance

Inheritance allows one class to inherit properties and methods from another class. This promotes code reuse and a hierarchical class structure.

Key point: Base class(parent class), the class whose properties and methods are inherited. Derived class(child class), the class that inherits properties and methods from the base class.

Example

python

1# Base class
2class Animal:
3    def __init__(self, name):
4        self.name = name
5
6
7    def make_sound(self):
8        print(f"{self.name} makes a sound")
9
10
11# Derived class
12class Dog(Animal):
13    def __init__(self, name, breed):
14        super().__init__(name)  # Call the constructor of the base class
15        self.breed = breed
16
17
18    # Override the method
19    def make_sound(self):
20        print(f"{self.name} barks!")
21
22
23# Derived class
24class Cat(Animal):
25    def make_sound(self):
26        print(f"{self.name} meows!")
27
28
29# Usage
30dog = Dog("Buddy", "Golden Retriever")
31cat = Cat("Whiskers")
32
33
34dog.make_sound()  # Output: Buddy barks!
35cat.make_sound()  # Output: Whiskers meows!

4. Polymorphism

Polymorphism allows objects of different classes to be treated as objects of a common super class. It enables the same method to perform different behaviours based on the object calling it.

Example of Method Overloading

python

1class Calculator:
2    def add(self, a, b, c=None):
3        if c is not None:
4            return a + b + c
5        else:
6            return a + b
7
8
9calc = Calculator()
10print(calc.add(1, 2))      # 3
11print(calc.add(1, 2, 3))   # 6

Example of Method Overriding

python

1class Animal:
2    def speak(self):
3        return "Animal makes a sound"
4
5
6class Dog(Animal):
7    def speak(self):
8        return "Dog barks"
9
10
11dog = Dog()
12print(dog.speak())  # Outputs: Dog barks

BankAccount Class

python

1class BankAccount:
2    def __init__(self, balance=0):
3        self.balance = balance
4   
5    def deposit(self, amount):
6        if amount > 0:
7            self.balance += amount
8        else:
9            raise ValueError("Deposit amount must be positive.")
10   
11    def withdraw(self, amount):
12        if amount > self.balance:
13            raise ValueError("Insufficient funds.")
14        self.balance -= amount
15   
16    def check_balance(self):
17        return self.balance

Shallow vs deep copy

Shallow copy: Copies the reference to object not the objects themselves
Deep copy: Copies the object and all nested objects, creating independent duplicates

python

1import copy
2
3list1 = [[1, 2], [3, 4]]
4shallow_copy = copy.copy(list1)
5deep_copy = copy.deepcopy(list1)
6
7list1[0][0] = 99  # Affects shallow_copy but not deep_copy

Data Structures and Algorithms

Stack

A stack is a linear data structure that follows the LIFO (Last in, First Out) principle. The last element added to the stack in the first one to be removed.

Common Operations:

Push: Add an element to the top of the stack.
Pop: Remove and return the top element from the stack.
Peek: View the top element without removing it.

Real-world example:

Think of a stack of plates. The last plate you put on the top is the first one you take off.
Usages: Undo functionality in software like text editors or drawing programs

Queue

A queue is a linear data structure that follows the FIFO(First in, First Out) principle. The first element added to the queue is the first one to be removed.

Common operations:

Enqueue: Add an element to the end of the queue
Dequeue: Remove an element to the first.

Real-world example:

Think of a line at a bank counter. The first person in line gets served first.
Usages: Printer queue (Jobs are prints in the order they arrive) or handling requests in a web server.

Example Stack and Queue

python

1class Stack:
2    def __init__(self):
3        self.items = []
4
5    def push(self, item):
6        self.items.append(item)
7
8    def pop(self):
9        return self.items.pop() if not self.is_empty() else None
10
11    def is_empty(self):
12        return len(self.items) == 0
13
14class Queue:
15    def __init__(self):
16        self.items = []
17
18    def enqueue(self, item):
19        self.items.insert(0, item)
20
21    def dequeue(self):
22        return self.items.pop() if not self.is_empty() else None
23
24    def is_empty(self):
25        return len(self.items) == 0
26
27# Example usage
28stack = Stack()
29stack.push(1)
30stack.push(2)
31print(stack.pop())  # Output: 2
32
33queue = Queue()
34queue.enqueue('a')
35queue.enqueue('b')
36print(queue.dequeue())  # Output: 'a'

Reverse a Linked List

Types

Singly Linked list: Each node points to the next node.
Doubly Linked list: Each node has pointers to both the next and previous nodes.

Implementing a Singly Linked List

python

1class Node:
2    def __init__(self, data):
3        self.data = data
4        self.next = None
5
6class SinglyLinkedList:
7    def __init__(self):
8        self.head = None
9
10    def insert(self, data):
11        new_node = Node(data)
12        if not self.head:
13            self.head = new_node
14        else:
15            current = self.head
16            while current.next:
17                current = current.next
18            current.next = new_node
19
20    def display(self):
21        current = self.head
22        while current:
23            print(current.data, end=" -> ")
24            current = current.next
25        print("None")
26
27# Example usage
28sll = SinglyLinkedList()
29sll.insert(1)
30sll.insert(2)
31sll.insert(3)
32sll.display()  # Output: 1 -> 2 -> 3 -> None

Reversing a Singly Linked list

To reverse a linked list, we need to iterate through the list and reverse the next pointers of the nodes so that they point to the previous node.

Example

python

1# Define a Node class
2class Node:
3    def __init__(self, data):
4        self.data = data
5        self.next = None
6
7
8# Function to reverse a linked list
9def reverse_linked_list(head):
10    prev = None
11    current = head
12   
13    # Iterate through the list
14    while current:
15        next_node = current.next  # Store the next node
16        current.next = prev       # Reverse the 'next' pointer
17        prev = current            # Move prev to current node
18        current = next_node       # Move to the next node
19   
20    # After the loop, prev will be the new head
21    return prev
22
23
24# Helper function to print a linked list
25def print_linked_list(head):
26    current = head
27    while current:
28        print(current.data, end=" -> ")
29        current = current.next
30    print("None")
31
32
33# Example Usage
34# Creating a linked list: 1 -> 2 -> 3 -> 4 -> None
35head = Node(1)
36head.next = Node(2)
37head.next.next = Node(3)
38head.next.next.next = Node(4)
39
40
41print("Original Linked List:")
42print_linked_list(head)
43
44
45# Reversing the linked list
46new_head = reverse_linked_list(head)
47
48
49print("Reversed Linked List:")
50print_linked_list(new_head)

Complexity

Time Complexity: O(n) where n is the number of nodes in the linked list (we visit each node once)
Space Complexity: O(1), because we only use a few extra pointers.

Quicksort Algorithm and Time Complexity

Steps

Pick a pivot: select a pivot element from the array(commonly the first, last or middle element or a random one)
Partitioning: Rearrange the array such that all elements less than the pivot are on the left side and all elements greater than the pivot are on the right side.
Recursion: Recursively apply the same process to the left and right sub-arrays
Base case: Stop when the sub-arrays contain only one element (already sorted).

Example

python

1def quicksort(arr):
2    # Base case: array is empty or has one element
3    if len(arr) <= 1:
4        return arr
5    else:
6        pivot = arr[len(arr) // 2]  # Choose the middle element as the pivot
7        left = [x for x in arr if x < pivot]   # All elements less than pivot
8        middle = [x for x in arr if x == pivot]  # All elements equal to pivot
9        right = [x for x in arr if x > pivot]  # All elements greater than pivot
10       
11        # Recursively apply quicksort to left and right sub-arrays
12        return quicksort(left) + middle + quicksort(right)
13
14# Example usage
15arr = [3, 6, 8, 10, 1, 2, 1]
16sorted_arr = quicksort(arr)
17print("Sorted Array:", sorted_arr)

Complexity

Time

Base case: O(n log n) occurs when the pivot consistently divides the array into balanced sub-arrays
Average case: O(n log n) as the array is usually split in a relatively balanced manner.
Worst case: O(n^2) occurs when the pivot divides the array into very unbalanced sub-arrays
Worst case example:
If the array is already sorted, and we always pick the first or last element as the pivot, we repeatedly partition the array into one large sub-array and one empty one, leading to O(n^2) behaviour.

Space

O(log n) Due to the recursion stack in the best and average cases.
O(n) in the worst case because of the recursion depth when the pivot leads to highly unbalanced partitions.

CRUD operations in SQL

CRUD operations in SQL refer to the basic operations we can perform on a database: Create, Read, Update, and Delete.

1. Create (INSEART)

sql

1CREATE TABLE Employees (
2    EmployeeID INT PRIMARY KEY,
3    FirstName VARCHAR(50),
4    LastName VARCHAR(50),
5    Salary DECIMAL(10, 2)
6);
7
8INSERT INTO Employees (EmployeeID, FirstName, LastName, Salary)
9VALUES (1, 'John', 'Doe', 50000.00);

2. Read (SELECT)

sql

1SELECT FirstName, LastName, Salary
2FROM Employees
3WHERE Salary > 40000;

3. Update(UPDATE)

sql

1UPDATE Employees
2SET Salary = 55000
3WHERE EmployeeID = 1;

4. Delete (DELETE)

sql

1DELETE FROM Employees
2WHERE EmployeeID = 1;

SQL Basics

JOIN

There are different types of joins, but the most common is the INNER JOIN, which returns only matching rows between two tables.

sql

1-- Table: Orders
2OrderID | CustomerID | OrderDate
3--------------------------------
41       | 1          | 2024-01-01
52       | 2          | 2024-02-01
6
7
8-- Table: Customers
9CustomerID | Name       | City
10------------------------------
111          | John Smith | New York
122          | Jane Doe   | Los Angeles
13
14
15-- INNER JOIN Example
16SELECT Orders.OrderID, Customers.Name, Orders.OrderDate
17FROM Orders
18INNER JOIN Customers ON Orders.CustomerID = Customers.CustomerID;
19
20
21-- Result
22OrderID | Name       | OrderDate
23--------------------------------
241       | John Smith | 2024-01-01
252       | Jane Doe   | 2024-02-01

GROUP BY and HAVING

Group by is used to group records with the same values.
Having is used to filter records after Group by is applied

sql

1SELECT City, COUNT(CustomerID) AS NumberOfCustomers
2FROM Customers
3GROUP BY City
4HAVING COUNT(CustomerID) > 1;

Aggregate Functions

sql

1-- Count the number of employees
2SELECT COUNT(*) AS TotalEmployees
3FROM Employees;
4
5
6-- Find the maximum salary
7SELECT MAX(Salary) AS HighestSalary
8FROM Employees;
9
10
11-- Find the average salary
12SELECT AVG(Salary) AS AverageSalary
13FROM Employees;
14
15
16-- Find the total salary cost
17SELECT SUM(Salary) AS TotalSalaryCost
18FROM Employees;

ACID Properties

ACID is an acronym that stands for Atomicity, Consistency, Isolation, and Durability. These are key properties of database transactions to ensure data integrity.

ACID Explained:

Atomicity: Ensures that all operations within a transaction are completed successfully, or none of them are. If one part of a transaction fails, the entire transaction is rolled back.
- Example: Transferring money from one bank account to another – either both accounts are updated, or none are.
Consistency: Ensures that a transaction brings the database from one valid state to another, maintaining all predefined rules (such as constraints, triggers).
- Example: If a field is marked as NOT NULL, no transaction should allow inserting a NULL value.
Isolation: Ensures that concurrent execution of transactions leads to the same state as if the transactions were executed sequentially.
- Example: If two users try to book the last seat in a cinema simultaneously, only one transaction should succeed.
Durability: Once a transaction has been committed, it remains so, even in the case of a system failure (e.g., power outage).
- Example: After transferring money, the updated balances should remain persistent even if the system crashes.

Basic AI Knowledge

Question: Explain the difference between supervised and unsupervised learning in machine learning.

Supervised Learning:

Uses labeled data
The algorithm learns to predict outputs based on input features
Examples: classification, regression
Use case: spam detection, price prediction

Unsupervised Learning:

Uses unlabeled data
The algorithm finds patterns or structures in the data
Examples: clustering, dimensionality reduction
Use case: customer segmentation, anomaly detection
Python example of supervised learning (Linear Regression):

python

1from sklearn.linear_model import LinearRegression
2import numpy as np
3
4# Sample data
5X = np.array([[1], [2], [3], [4], [5]])
6y = np.array([2, 4, 5, 4, 5])
7
8# Create and train the model
9model = LinearRegression()
10model.fit(X, y)
11
12# Make a prediction
13print(model.predict([[6]]))  # Predict for X = 6

Analytical Skills

Question: Given a scenario: "A city wants to optimize its traffic light system to reduce congestion." Describe your approach to analyzing this problem and proposing a solution.

Approach:

Data Collection:

Traffic flow patterns
Peak hours and congestion points
Current traffic light timings

Analysis:

Identify bottlenecks and high-congestion areas
Analyze the relationship between light timings and traffic flow

Propose Solution:

Implement an AI-based adaptive traffic control system
Use real-time data from sensors and cameras
Dynamically adjust light timings based on current traffic conditions

Implementation:

Start with a pilot program in high-congestion areas
Use machine learning algorithms to continuously improve the system

Evaluation:

Compare traffic flow before and after implementation
Measure reduction in average wait times and overall congestion

These may not be enough, but they cover 70-80% of frequently asked topics. Start with these related topics. If you plan on applying, learn more about these areas.

Thank you very much for reading my blog. 🙌

Table of contents

Common Topics for Software Development Interviews and Written Tests in Bangladesh, 2024

For write code on pen and paper without an IDE

1. Prime Number Check

2. Leap Year Calculation

3. Fibonacci Sequence

4. Factorial Calculator

5. Palindrome Checker

6. Armstrong number

7. Greatest Common Divisor (GCD)

8. Sum of Digits

9. Reverse a String

10. Bubble Sort

11. Binary Search

12. Find Max value in array

13. Write a Python function to find the second largest number in a list.

14. Remove duplicate in array

14.1 Using List Comprehension with enumerate

15. Swap value using a temporary variable

OOP

1. Encapsulation

Example

2. Abstraction

Example

3. Inheritance

Example

4. Polymorphism

Example of Method Overloading

Example of Method Overriding

BankAccount Class

Shallow vs deep copy

Data Structures and Algorithms

Stack

Common Operations:

Real-world example:

Queue

Common operations:

Real-world example:

Example Stack and Queue

Reverse a Linked List

Types

Implementing a Singly Linked List

Reversing a Singly Linked list

Example

Complexity

Quicksort Algorithm and Time Complexity

Steps

Example

Complexity

Time

Space

CRUD operations in SQL

1. Create (INSEART)

2. Read (SELECT)

3. Update(UPDATE)

4. Delete (DELETE)

SQL Basics

JOIN

GROUP BY and HAVING

Aggregate Functions

ACID Properties

ACID Explained:

Basic AI Knowledge

Supervised Learning:

Unsupervised Learning:

Analytical Skills

Approach:

Common Topics for Software Development Interviews and Written Tests in Bangladesh, 2024

For write code on pen and paper without an IDE

1. Prime Number Check

2. Leap Year Calculation

3. Fibonacci Sequence

4. Factorial Calculator

5. Palindrome Checker

6. Armstrong number

7. Greatest Common Divisor (GCD)

8. Sum of Digits

9. Reverse a String

10. Bubble Sort

11. Binary Search