Low-Level Design Interview Questions for Freshers and Experienced Candidates - IQCode (2023)

Importance of Low-Level Design (LLD)

Developing software requires several steps, including identifying the business problem, collecting functional requirements, designing a system architecture, coding, testing, deployment, and maintenance. However, before coding, it's essential to perform two crucial steps: High-Level Design (HLD) and Low-Level Design (LLD).

LLD holds significant importance as it involves designing each component in detail, categorizing classes, using abstractions, demonstrating data flow between different objects, etc. LLD transforms the high-level design into detailed design components that are ready to code.


It's essential to have a thorough understanding of LLD concepts, design patterns, and best practices while preparing for an LLD interview. Freshers are advised to refer to coding examples and seek help from experienced professionals to get started with LLD. On the other hand, experienced candidates must be proficient in design patterns, software architecture, and real-time problem-solving to ace an LLD interview.


Some common LLD interview questions are as follows: - Explain the Singleton design pattern - Design a parking lot system using OOP concepts - Design a movie ticket booking system using UML diagrams - Explain the various types of database normalization - Implement a data structure that supports insertion, deletion, and accessing the minimum element in O(1) time complexity.


During an LLD interview, it's crucial to communicate your thought process audibly and logically. Ensure that your design is modular, scalable, and maintainable. It's better to ask clarifying questions before starting to solve the problem. Also, having a working prototype ready to demonstrate could be a plus point. Finally, prepare well on LLD concepts and have confidence in your problem-solving abilities.

Tips for Preparing for Low-Level Design Interviews

When preparing for low-level design interviews, there are several things that you can do to increase your chances of success:

1. Review the basics of data structures, algorithms, and coding principles. You should have a good understanding of common data structures like linked lists, stacks, queues, and trees, as well as basic sorting and searching algorithms.

2. Practice coding problems that relate to low-level design. You can find practice problems on websites like LeetCode, HackerRank, and CodeSignal. Make sure to practice designing systems that can scale and handle large amounts of data.

3. Familiarize yourself with object-oriented design principles. You should be able to identify when to use inheritance, encapsulation, and polymorphism in your designs.

4. Be prepared to discuss your design decisions. During the interview, the interviewer is looking for someone who can explain their thought process and justify their design decisions.

5. Practice problem-solving under pressure. Your interviewer may ask you to solve a coding problem under time pressure, so it's important to practice working quickly and efficiently.

By following these tips, you can prepare yourself for low-level design interviews and increase your chances of success. Good luck!

Tips for Solving Low-Level Design Problems in Interviews

When faced with low-level design problems during an interview, there are several tips that can help you solve them effectively:

//Start by understanding the problem thoroughly

//Identify the key components and their relationships

//Think of possible solutions and compare them for efficiency, memory usage, and overall effectiveness

//Simulate the design by drawing diagrams or creating sample code if possible

//Consider edge cases and constraints, and ensure the design can handle them

//Communicate your thought process and approach clearly to the interviewer

Designing a Snake and Ladder Game

To design a Snake and Ladder game, we can start by creating a board with 100 cells arranged in a 10x10 grid. Each cell will represent a position on the board. We can then add snakes and ladders to the board, which will connect different cells and add an element of chance to the game.

We can use a random number generator to simulate the roll of a dice, which will determine the number of cells a player moves forward on the board. We can then check if the player has landed on a snake or a ladder, and move them to the appropriate cell.

To keep track of the players' positions, we can create a Player class with a current position variable. We can also keep track of the number of rounds played and the winner of the game.

Here's some sample code to get started:

class Player:
    def __init__(self, name):
        self.name = name
        self.current_position = 0
class Board:
    def __init__(self):
        self.cells = [i for i in range(101)]
        self.snakes = {17: 7, 54: 34, 62: 19, 98: 79}
        self.ladders = {3: 38, 24: 33, 42: 93, 72: 84}

    def move_player(self, player, steps):
        old_position = player.current_position
        new_position = old_position + steps

        # Check if player has landed on a snake or ladder
        if new_position in self.snakes:
            new_position = self.snakes[new_position]
        elif new_position in self.ladders:
            new_position = self.ladders[new_position]

        # Update player position
        player.current_position = new_position

    def play_game(self, players):
        num_players = len(players)
        current_player_index = 0
        winner = None
        rounds_played = 0

        while not winner:
            current_player = players[current_player_index]
            steps = random.randint(1, 6)
            self.move_player(current_player, steps)
            # Check if player has won
            if current_player.current_position == 100:
                winner = current_player
            # Move on to next player
            current_player_index = (current_player_index + 1) % num_players
            rounds_played += 1

        print(f"{winner.name} won in {rounds_played} rounds!")

We can create a Board object and a list of Player objects to play the game:

board = Board()
player1 = Player("Alice")
player2 = Player("Bob")
players = [player1, player2]


This should output the name of the winner and the number of rounds played. Note that we have only implemented the basic rules of the game, and there are many variations and additional features that can be added to make the game more interesting.

Tips for Preparing for a Low-Level Design (LLD) Interview

Here are some helpful tips for preparing to ace your Low-Level Design (LLD) interview:

1. Brush up on your basics: Make sure you have a strong understanding of computer science fundamentals such as data structures, algorithms, operating systems, and databases.

2. Know the programming languages and tools required for the job: Research the primary programming languages and tools used in the role you are interviewing for and be prepared to discuss them in depth.

3. Familiarize yourself with system design patterns: Understanding and being able to implement system design patterns is important in LLD interviews. Review common patterns like Singleton, Decorator, and Facade.

4. Develop your problem-solving skills: Practice coding challenges and problem-solving exercises to strengthen your skills and build your confidence.

5. Practice communication: Be prepared to discuss and explain your designs and solutions clearly and concisely, highlighting any tradeoffs or considerations that you took into account.

Remember, preparation is key to success in any interview. Good luck!Sorry, it is not clear what you mean by "Act like API". Could you please provide more context or information?Title: How to Write Code that Mimics an API

When writing code that mimics an API, it is important to make sure that it is both efficient and easy to use. This can be achieved by following certain guidelines and best practices.

// Start by defining your API endpoints and the data that will be returned
const endpoint1 = "https://api.example.com/endpoint1";
const endpoint2 = "https://api.example.com/endpoint2";
const data = {
  name: "John Doe",
  age: 30,
  email: "[email protected]"

// Create functions for each endpoint that fetch data from the server
function getEndpoint1() {
  return fetch(endpoint1)
    .then(response => response.json())
    .catch(error => console.error(error));

function getEndpoint2() {
  return fetch(endpoint2)
    .then(response => response.json())
    .catch(error => console.error(error));

// Export the functions as a module
export { getEndpoint1, getEndpoint2 };

By defining the API endpoints and data at the beginning of the code, it is easier to manage and modify as needed. Using the


method to retrieve data from the server simplifies the code and allows for easy error handling using


. Exporting the functions as a module makes it easy for other developers to use in their own code.

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