Navigating the Coding Interview: Tips for Success

Introduction to Coding Interview Preparation

A coding interview is a part of the hiring process of most tech companies. It is used to test the candidate's technical and critical-thinking skills to solve any problems. Furthermore, through the coding interview, the employer also checks the logic-building ability of the candidates.

In such type of technical interview, 2 to 5 coding interview questions are given to the candidate to solve them in the limited time and prove their ability. However, these questions' levels can be different, like easy, medium, and hard.

Before you go for the coding interview for any company, it is necessary to understand what kind of coding interview questions they are asking to crack the interview. As you can't crack the interview by solving 50 to 100 coding questions, you need to understand the concepts behind the question to solve it.

If you are a fresher and want to land a dream job in the dream company as a software developer, this guide can be helpful in preparing for your next coding interview. However, this guide will also help the experienced software developer applying for new jobs.

Why Coding Interviews Can Be Challenging

In the competitive world, there were 23.7 million software developers in 2018, which increased to 27.7 million in 2023 in the world. So, competition for jobs is increasing.

You should have the perfect skills to crack coding interviews to get high-paying jobs. Every day, tech companies get many applications for new joiners. So, they are making coding interview questions more challenging to hire the best candidates.

Here are a few reasons why coding interviews are becoming challenging.

• Time pressure: In the coding interview, the candidate is required to solve the given problem in the specified time. Sometimes, a candidate may make mistakes in identifying the concept of the problem and solving it quickly.
• Unfamiliar Problems: In the coding interview of the big tech companies, they never ask repetitive questions. However, they ask the question of the same concept. If you are well-prepared with a particular concept, you can easily solve the problem.
• Debugging and testing: In some coding interviews, companies give you questions and their solution containing the bug. After that, you need to identify the bug and submit the correct solution. So, debugging and testing the code in the given time constraint is also challenging.
• Programming language: Choosing a programming language is also challenging, as some companies ask interviewers to solve the problem in a specific language.

Now, let's start with how you can start preparing for your upcoming coding interview.

Understanding the Types of Coding Interview Questions

Each company has a different interview policy. Some companies ask only technical coding interview questions, and some companies ask only Concept-based Coding Interview questions. However, some companies ask both types of questions.

Here, you will understand the examples of the technical and concept-based coding interview questions.

Technical Coding Interview Questions

Companies can test your problem-solving skills using technical coding interview questions.

In the technical coding questions, you will have given 2 to 3 lines of problem statement, sample input, and output. After that, you are required to write code in any particular programming language to solve the problem.

Let's take an example of the technical coding interview question.

Problem Statement: Given an integer array nums, return true if any value appears at least twice in the array, and return false if every element is distinct.

Example 1:

Input – nums = [10, 20, 30, 40, 50]
Output – false
Explanation – The array contains only unique elements.

Example 2:

Input – nums = [10, 20, 30, 40, 40]
Output – true
Explanation – The array contains 40 two times.

Algorithm:

• Get the length of the array.
• Traverse through each element of the array using the loop.
• Use a nested loop to traverse array elements in the range of (i + 1, n) index, where ‘i’ is the iterator variable of the outer loop, and n is the array length.
• In the inner loop, if nums[i] and nums[j] are equal, return true.
• At last, return false from the function.

Solution:

def containsDuplicate(nums):
    n = len(nums)
    for i in range(n):
        for j in range(i + 1, n):
            if nums[i] == nums[j]:
                return True
    # If the loop completes without finding duplicates, return False
    return False

nums = [10, 20, 30, 40, 40]
result = containsDuplicate(nums)
print(result)

Time complexity: O(N*N) Space complexity: O(1)

You can solve each problem in multiple ways. For example, you can optimize the above code by using the set or hashmap and write a code with the O(N) time and O(N) space complexity.

Tech companies generally ask for an optimized solution; if you submit the unoptimized code, they don’t accept it.

Concept-based Coding Interview Questions

The concept-based coding interview questions are used to test your knowledge of computer science fundamentals. It contains the conceptual theory questions. However, companies can also give code of any programming language and ask to predict the output of the code to test your knowledge about programming language.

Let’s understand it via the example below.

Example:

You need to predict the output of the code below.

# Define a string
text = "Hello, "
# Multiply the string to repeat it multiple times
result = text * 3
# Print the result
print(result)

Output:

Hello, Hello, Hello, 

If you are not familiar with Python, you can’t predict the output.

However, some companies can also ask questions about system design, operating systems, database management systems, etc.

Furthermore, companies also ask to dry-run the given algorithm and predict the output for the given input.

Essential Topics for Coding Interviews

From this section, the actual guide starts with how to prepare for the coding interview. All you need to do is that you should be familiar with coding concepts.

Even if you have practiced 1000+ coding questions before sitting in the interview, and if you can’t solve the question given in the coding interview, all your efforts and hard work won’t appreciated.

So, it is important to identify the concept or pattern of the coding interview question first and find a solution for that in the next step.

Here, I have covered some concepts that you should prepare to crack technical coding interviews.

Data Structures

In computer science, data structure is essential for storing and manipulating data. The data structure handles how data is stored and accessed from the memory of the computer.

If you don’t know how to build a web page, you can land the job, but if you don’t know the data structure, you can’t be a software developer.

To become a software developer, you should have knowledge of at least 3 to 4 data structures like array, string, linked list, etc. However, you should know how each data structure works, stores data in the computer memory, and accesses data from it.

For example, a hash set allows you to access data in O(1) time, and an array or linked list allows you to access data in O(N) time.

However, it is a plus point if you know the advanced data structures like stack, queue, tree, graph, etc.

Algorithms

The algorithm is also important, like data structures. The algorithm tells how code should be executed. You can use different algorithms to solve a single problem.

For example, if you want to search for an element in the array, you can use the linear search or binary search algorithm. The binary search algorithm is more efficient as its time complexity is O(logN), and the time complexity of the linear search algorithm is O(N).

So, algorithms are important to optimize your code. When you search anything on Google, it gives you results in a fraction of the data. The answer is simple: they use a well-optimized search algorithm.

Similarly, you should create an algorithm before starting to write a solution code for any problem.

Data Structures and Algorithms Example

The companies can ask technical coding questions of particular data structures, as shown below.

Here, I have given a single coding interview question for each data structure.

1. Array

Problem: You have given an array containing different integers. You need to find the largest contiguous subarray with the maximum sum.

Example:

Input – nums = [-10, 5, 2, -2, 2, -13]
Output – 7
Explanation – The largest contiguous subarray with maximum sum is [5, 2, -2, 2].

Algorithm:

• Initialize the curr_sum variable with 0 and max_sum with minimum integer value.
• Traverse through the array.
• Add array element to curr_sum. If curr_sum is negative, initialize it with 0.
• Update the max_sum if curr_sum is greater than max_sum.
• Return max_sum at last.

Solution:

def maxSubArray(nums):
  curr_sum = 0
  max_sum = float('-inf')
  
  for n in nums:
    curr_sum += n
    if curr_sum < 0:
      curr_sum = 0
    max_sum = max(max_sum, curr_sum)
        
  return max_sum
  
nums = [-10, 5, 2, -2, 2, -13]
result = maxSubArray(nums)
print(result)

Time Complexity: O(N) Space Complexity O(1)

2. String

Problem: Given a string sentence containing English letters (lower- or upper-case), return true if the sentence is a Pangram or false otherwise. A Pangram is a sentence where every letter of the English alphabet appears at least once. Example:

Input – “abceio”
Output – “obciea”
Explanation – The sentence doesn’t contain each letter of the alphabet, so it is not a pangram.

Algorithm:

• Create a set to store all unique alphabetical characters.
• Convert string into lowercase.
• Start traversing the lowercase string.
• If a character is an alphabetical character, add it to the set.
• If the set contains 26 characters, return true. Otherwise, return false.

Solution:

def isPangram(sentence):
    unique_letters = set()
    sentence = sentence.lower()
    for char in sentence:
        if 'a' <= char <= 'z':
            unique_letters.add(char)
    return len(unique_letters) == 26

sentence = "The quick brown fox jumps over the lazy dog"
result = isPangram(sentence)
print(result)

Time Complexity: O(N)
Space Complexity: O(1)

3. Stack

Problem: Given a string containing the ‘(‘ and ‘)’ parenthesis. Check whether the string is a valid parentheses sequence. A sequence is valid if each opening bracket has a closing bracket. Return Boolean value, representing whether the sequence is valid.

Example:

Input –  str = ‘()(()’
Output – False
Explanation – There is no closing parenthesis for the third open parenthesis.

4. Queue

Problem: You have given a string and need to find the index of the first unique character in the string.

Example:

Input – str = “Designguru”
Output – 0
Explanation – ‘D’ is the first unique character in the string.

5. Linked List

Problem: You have given a linked list. Reverse the linked list.

Example:

Input – list = 10 -> 20 -> 30 -> 40 -> NIULL;
Output – 40 -> 30 -> 20 -> 10 -> NULL;
Explanation – Reversed the linked list.

6. Tree

Problem: You have given the root of a binary tree. You need to return its maximum depth.

Example:

Input – 
     1
    / \
   2   3
Output – 2
Explanation – The binary tree contains two levels only.

The Role of Recursion in Coding Problems

The recursion is a fundamental concept in the programming. It plays a significant role in solving various coding problems.

The recursion is a technique in which the function invokes itself multiple times until it reaches the base case. When it reaches the base case, it stops the execution of the code. Otherwise, it makes a function call for smaller input.

The recursion is used in the below concepts.

• Divide and conquer – The recursion divides the problem into smaller tasks and executes the algorithm for the divided task separately. After getting the result, it merges the results.
• Backtracking – When you are required to try all combinations of array elements or string characters, etc., you need to use backtracking. You can do backtracking using recursion.
• Dynamic programming – In dynamic programming, you break the problem into subproblems and solve every subproblem. So, you can recursively break each subproblem into the further subproblem and solve the problem quickly.

However, whatever problem you can solve using the recursion, you may also solve using the iterative approach.

The example problem for recursion is given below.

Problem: Find Nth Fibonacci number.

Example:

Input – N = 4
Output – 3
Explanation – The 4th Fibonacci number is 3.

Algorithm:

• If n is less than or equal to 0, return 0. It is a base case.
• If n is 1, return 1. It is also a base case.
• Otherwise, call the fibonacci_recursive() function for n – 1 and n – 2 and sum their returned value.
• Return the resultant sum.

Solution:

def fibonacci_recursive(n):
    if n <= 0:
        return 0
    elif n == 1:
        return 1
    else:
        return fibonacci_recursive(n - 1) + fibonacci_recursive(n - 2)

result = fibonacci_recursive(4)
print(result) 

To learn more about recursion, you can enroll in the Groking the Art of Recursion for Coding Interviews course.

Sorting and Searching Algorithms

The sorting and searching algorithms are the most popular concepts, and most companies ask at least 1 question in their technical coding interview.

Multiple searching and sorting algorithms are available, with a time complexity of O(N*N) to O(NlogN).

Let’s look at each searching and sorting algorithm.

Linear Search

• Traverse through array elements or string characters using a loop.
• If the array element or string character matches with the required one, return the index value.

Binary Search

The binary search algorithm is only used to search in the sorted data.

• Sort the list.
• Find the middle element of the current subarray.
• If the middle element is the target element, return the index of the middle element.
• If the middle element is greater than the searching element, recursively search in the left subarray.
• Otherwise, recursively search in the half subarray.

Bubble sort

The bubble sort works by swapping the list elements.

• Use two nested loops to traverse the list.
• If the element at the ith index is greater than the element at the jth index, swap both elements.
• Repeatedly swap all elements until the list is not sorted.

You can’t use the bubble sort algorithm to sort large lists as its time complexity is O(N2).

Merge sort

The merge sort is one of the efficient sorting algorithms, and its time complexity is O(NlogN).

• Divide the list into two halves.
• Sort both halves and merge them.
• Similarly, divide the sub-halves, sort them, and merge them.

The merge sort works on the divide and conquer approach.

There are also other sorting techniques available like selection sort, quick sort, counting sort, heap sort, insertion sort, etc.

Preparing for Specific Company Interviews: The FAANG Example

Every software developer's dream is to get a job in the FAANG (Facebook, Amazon, Apple, Netflix, Google) companies. Due to these companies' balance and productive work culture, everyone wants to work for them. Another advantage is high paying salaries, which every developer wants.

Follow the steps below to prepare for the FAANG company’s interview.

Do Research

It is necessary to research the job role and the company's interview process for a particular job role. It implies the preparation of interviews of each company, not only FAANG companies.

Each company has a different interview process for different Job roles. For example, some company has 5 to 7 rounds, including 3 coding rounds.

Get prepared With Tech Skills

After the research about the interview process, the next step is to work on improving the required technical skills to crack the interview.

You may be required to work on the below technical skills.

• Improve DSA & algorithm concepts.
• Work on system design
• Prepare for the behavioral question.
• Solve as many coding problems as possible and achieve a strong foundation in each concept.
• Prepare core CS subjects.

Examples of Questions Asked in FAANG Interviews

Here, I have given sample questions asked in previous interviews of the FAANG companies.

Coding Questions

Problem: You have given an array containing multiple integers and a single integer value called targeted. You need to find two indices of the array so that their element’s sum equals the target integer.

Example:

Input – nums = [4, 7, 9, 2], target = 9  
Output – [2, 4]  
Explanation – The sum of 7 and 2 is 9.  

Algorithm:

• Define the num_map dictionary to store the array element and its index.
• Traverse the nums array using loop.
• In the loop, store the target – n into the complement.
• If complement exists in the num_map, return the complement index and current index.
• Store the current array element and index into the num_map.

Solution:

def twoSum(nums, target):
  num_map = {}
  for i, n in enumerate(nums):
    complement = target - n
    if complement in num_map:
      return [num_map[complement], i]
    num_map[n] = i
    
nums = [4, 7, 9, 2];  
target = 9  
result = twoSum(nums, target)
print(result)

Merge K Sorted List Problem: Given an array of linked lists lists, merge all the lists into one sorted list.

Example:

Input – lists = [[6, 7, 9],[1, 2, 5],[3, 8]]
Output – [1, 2, 3, 5, 6, 7, 8, 9]
Explanation – Merged all 3 lists together in the sorted order.

System Design Questions

Question: How would you design a social media post recommendations system?

Approach: The main goals are to suggest relative post. Suggest newer or fresh content, ask users what they like and don’t like, and rank posts based on user’s opinions. Ranking algorithms can be optimized based on the cached data of users.

Question: How would you design a chat system app?

Approach: Requirements: Online, multi-functional, protected, etc. You can discuss the app's consistency. Furthermore, you can talk about the application's low latency and high availability.

Behavioral Questions

Question: Discuss the most difficult project in your last organization.

Approach: You may discuss any challenging project and difficulties faced in that. You may talk about why you faced difficulties. For example, due to limited knowledge of concepts, programming languages, etc. At last, don’t forget to tell an interviewer how you have overcome the challenge.

Question: How do you maintain a good work-life balance?

Approach: You can tell the interviewer that by prioritizing the task, taking regular breaks, utilizing technology wisely, and collaborating with teammates.

Common Questions Based on Programming Languages

Sometimes, interviews ask language-specific questions in the mock interview. You should be prepared for that.

Here, I have given 5 questions for Java and Python.

Java Interview Questions

1. What is Java? Java is a high-level object-oriented programming language., developed by the Sun microsystem in 1991. It is a multi-threaded, platform-independent, and high-performance programming language. Now, Oracle is handling the Java.

2. What is JVM? JVM is an acronym for the Java Virtual Machine. It is a part of the Java runtime environment. JVM interprets and translates the high-level Java code into the Machine-specific byte code. So, that Java program can be run on any platform independently.

3. Is delete, next, and main keyword in Java? In Java, delete and next is not a keyword, but ‘main’ is a keyword. The ‘main’ keyword is used to define the main method, which is a starting point of the Java code.

4. What is the main difference between Java and C++? The main difference between Java and C++ is that memory management. Java has an automatic garbage collection mechanism, but C++ doesn’t. C++ supports the pointers, but Java doesn’t support the pointers. In C++, you can achieve multiple inheritance, but in Java, you need to use the interface to achieve multiple inheritance.

5. What keyword do you use to define Boolean types of variables in Java? In Java, you can use the ‘boolean’ keyword to declare the Boolean type of the variable.

Python Interview Questions

1. What is Python? Python is a high-level programming language like Java and C++. The first version of Python was released in 1991 by Guido van Rossum. It is known for its simplicity. It also supports the object-oriented programming language. Python is widely used in domains like data science, Artificial intelligence, web development, game development, Android and IOS development, Machine learning, Deep learning, etc.

2. Is Python a compiled language or an interpreted language? Python is partially interpreted and partially compiler language. Python can use the interpreter to execute the code directly line-by-line. However, it can also compile the code into the byte code, and the interpreter can execute it after that.

3. Which symbol is used to comment the code in Python? In Python, the ‘#’ (hash) symbol can add the comment in the code. The Python interpreter considers whatever you write after the ‘#’ symbol as a comment.

4. What is the use of the ‘self’ in Python? The ‘self’ is a parameter used with the instance methods. It refers to the instance of the class. You can use it to access the class elements.

5. What is a namespace in Python? In Python, a Namespace is a container used to avoid conflicts between identifiers.

Recommended Resources for Further Preparation

There is no shortcut to crack the coding interviews. You need to do hard work and clear all concepts required to crack the coding interview.

Here, I have recommended some courses and online platforms that you can use for further preparation for your next interview.

Data Structure and Algorithm Courses

Here are the courses you may enroll in to prepare for DSA.

1. Coding Interview RoadMap By DesignGuru

The coding interview roadmap course is prepared by the Design Guru. It contains the coding questions of different levels according to the concept.

It covers all concepts related to the data structure and algorithm. Also, solutions to each coding question are provided. You can try some free concepts; if you like them further, you may enroll.

2. Complete Interview Preparation By GeeksForGeeks

This course is prepared by the experts of the GeeksForGeeks team. The course contains a full road map for the interview preparation. It also contains the DSA section, containing the DSA problems based on the concepts.

Recommended Reading and Online Platforms

Here are the recommended platforms that you can use for the coding interview preparation.

1. Leetcode

Leetcode is one of the best online platforms to practice DSA and algorithm questions. You can find different problem levels and solve them according to your capabilities.

Furthermore, Leetcode allows you to filter the coding questions based on various categories.

2. DesignGuru

The Design Guru contains multiple DSA questions according to the category of the questions. You can pick any and try to solve them. Also, they have a built-in code editor. So, you can practice the questions on their website.

Conclusion: Action Points for Effective Preparation

I hope you got enough information and tips about cracking the coding interviews. You should solve as many coding interview questions as you can. You can also enroll in self-paced courses to get a proper road map for the interview process.

Furthermore, you should set the goals and milestones in the interview preparation process and continuously track them.