70+ Coding Interview Questions for Software Engineers and Developers in 2025

There are a lot of computer science graduates and programmers applying for programming, coding, and software development roles at startups like Uber and Netflix and big organizations like Amazon, Microsoft, and Google. They are also quite popular on service-based companies like Infosys, TCS, or Luxsoft, but many of them have no idea of what kind of programming interview questions to expect when you’re applying for a job with these companies. Things have also changed a lot in the last few years and coding interviews have become tougher. Now you need to go through a couple of coding interview rounds but you also need to prepare for System design problems which wasn’t normal in the last decade.

Top 10 Algorithms books Every Programmer Should Read

Algorithms are language agnostic, and any programmer worth their salt should be able to convert them to code in their programming language of choice. Unfortunately, I have come across several programmers who are REALLY good at programming languages like Java or Python, like know minor details of API and language intricacies but have very poor knowledge of the fundamentals of Algorithms and Data Structures. Just ask them to implement any popular sorting algorithms like quicksort or merge sort, and they will fall apart. If you expect them to know more advanced and sophisticated algorithms like String processing algorithms, graph algorithms, tree traversal, or greedy algorithms, be ready to check on Interviews; otherwise, you might end up with some surprises.

How to implement Level Order Traversal of Binary Tree in Java? Example Tutorial

Hello guys, if you have worked in Java then you know that binary tree is one of the essential data structure and quite an important one for programmers, I even mentioned that on my 10 essential data structures for programmers articles. Binary tree related question are also quite common on coding interviews and we are going to see one today but before that, let's revise what is binary tree? Binary trees are hierarchical data structures composed of nodes, each having at most two children: a left child and a right child. Traversing a binary tree in level order involves visiting nodes level by level, starting from the root.

How to Implement Binary Tree InOrder traversal in Java without Recursion - Example Tutorial

I have been writing about different binary tree traversal algorithms and so far we have seen both pre-order and post-order algorithms to traverse a binary tree and today you'll learn about the in-order or sorted order algorithms. This is actually the second part of implementing the inorder traversal of a binary tree in Java, in the first part, I have shown you how to solve this problem using recursion and in this part, we'll implement the inorder traversal algorithm without recursion. Now, some of you might argue, why use iteration if the recursive solution is so easy to implement? Well, that's true, but the iterative solution is often regarded better as they are not prone to StackOverFlowError. Another reason why we are discussing the iterative solution here is because of technical interviews.

How to remove duplicate characters from String in Java? [Solved]

Hello all, how are you doing? It's been a long since I have shared a coding problem from the interview. The last one I discussed was about finding the Nth Fibonacci number, one of the popular dynamic programming problems. Never mind, today, you are going to learn about another popular coding problem. How do you remove duplicate or repeated characters from String in Java is one of the frequently asked string-based coding problems from Interviews. This problem is very similar to removing duplicate elements from an array which we have discussed in the past here after all String is a character array in Java. If you know how to solve that problem, you should be able to solve this one as well.

How to find median of two sorted arrays in Java? Example Tutorial

Hello friends, we meet again on our journey of Java and the ocean of knowledge. I am sure you guys must be very excited about today's lesson as today we will deep dive into something that makes everyone's head scratch, yes, we will talk about a popular coding problem. So friends, get ready to scratch your head, learn something, code a few things, and use some of your grey cells (Agatha christie fans rejoicing in the back :p). So friends, today's topic is coding and we will take on one of the most famous and difficult problems. Today we will learn how to find the median of two sorted arrays. seems easy right? Wait a bit, I will make sure you learn something new and make it a bit of a challenge :D

Fibonacci Series in Java Using Recursion

Fibonacci series in Java
Write a Java program to print the Fibonacci series up to a given number or create a simple Java program to calculate Fibonacci number is common Java questions on fresher interviews and homework. Fibonacci series is also a popular topic on various programming exercises in schools and colleges. Fibonacci series is a series of natural numbers where the next number is equivalent to the sum of the previous two numbers like fn = fn-1 + fn-2. The first two numbers of the Fibonacci series are always 1, 1. In this Java program example for the Fibonacci series, we create a function to calculate Fibonacci numbers and then print those numbers on the Java console.

How to Reverse an Integer in Java without converting to String? Example and Solution

Hello guys, LeetCode has a problem reversing digits of an integer number without using any library method like the reverse() method of StringBuffer. In LeetCode, you can solve this problem with many different languages like Java, C, C++, C#, Python, Ruby, and even JavaScript. Btw, in the article, you will learn how to solve this problem in Java. Before approaching a solution let's first read the problem statement :

Reverse digits of an integer.

Example 1: x = 123, return 321
Example 2: x = -123, return -321

How to Find Nth Fibonacci Number in Java [Solved] - Example Tutorial

It's been a long time since I have discussed a coding problem in this blog. So, I am going to start with probably the oldest one of them, how do you find the nth number in a Fibonacci sequence? or how do you find the Fibonacci number in Java? or maybe printing the Fibonacci series. If you are a regular reader of this blog then you might know that I have already discussed both recursive and iterative algorithms for printing the Fibonacci series but never really discussed especially writing a program to return the Nth Fibonacci number in Java. Don't worry the wait is over as in this article, we'll solve this common problem and learn a bit more about problem-solving, recursion, iteration, and some basic algorithm skills.

How to implement Linear Search Algorithm in Java? Example tutorial

In the last article about searching and sorting, you have learned the binary search algorithm and today I'll teach you another fundamental searching algorithm called Linear search. Linear search is nothing but iterating over the array and comparing each element with the target element to see if they are equal since we search the array sequential from start to end, this is also known as sequential search or linear search. It is very slow as compared to binary search because you have to compare each element with every other element and is definitely not suitable for a large array. It's practically useful only in the case of a small array of up to 10 to 15 numbers. In the worst case, you need to check all elements to confirm if the target element exists in an array or not.

How to implement Radix Sort in Java - Algorithm Example [Solved]

The Radix sort, like counting sort and bucket sort, is an integer-based algorithm (I mean the values of the input array are assumed to be integers). Hence radix sort is among the fastest sorting algorithms around, in theory. It is also one of the few O(n) or linear time sorting algorithms along with the Bucket and Counting sort. The particular distinction for radix sort is that it creates a bucket for each cipher (i.e. digit); as such, similar to bucket sort, each bucket in radix sort must be a growable list that may admit different keys.

How to implement Merge Sort Algorithm in Java [Solved] - Example Tutorial

The merge sort algorithm is a divide and conquers algorithm. In the divide and conquer paradigm, a problem is broken into smaller problems where each small problem still retains all the properties of the larger problem -- except its size. To solve the original problem, each piece is solved individually; then the pieces are merged back together. For example, imagine you have to sort an array of 200 elements using the bubble sort algorithm. Since selection sort takes O(n^2) time, it would take about 40,000-time units to sort the array. Now imagine splitting the array into ten equal pieces and sorting each piece individually still using selection sort. Now it would take 400-time units to sort each piece; for a grand total of 10*400 = 4000.

Counting Sort in Java - Example

The Counting sort algorithm, like Radix sort and Bucket sort, is an integer-based algorithm (i.e. the values of the input array are assumed to be integers), non-comparison, and linear sorting algorithm. Hence counting sort is among the fastest sorting algorithms around, in theory. It is also one of the few linear sorting algorithms or O(n) sorting algorithms. It's quite common in Java interviews nowadays to ask, whether do you know any O(n) sorting algorithm or not. If you face this question in the future, you can mention Radix sort, Bucket sort, or Counting sort algorithms.

How to use Deque Data Structure in Java? Example Tutorial

Hello friends, I am really glad to see you all again here. And I know you are here to learn new and valuable Java concepts and continue your journey on Java. Today we are gonna learn something that is really important logically. yes! you heard right, we are going to learn about Deque data structure in Java and how to use Deque in the Java program. Deque is a special data structure, a double-ended queue that allows you to process elements at both ends, I mean you can add and remove objects from both front and rear end. It's a short form of Double-Ended Queue and pronounced as "Deck".

How to find Kth Smallest Element in a Binary Search Tree? [Solved]

Hello guys, I have been sharing binary search tree-based coding interview questions for quite some time. In the last article, we looked at how to find the maximum sum level in a given binary tree, and in this article, we will find the kth smallest number in a given binary tree like the 5th smallest or 3rd smallest number. Before we find the kth smallest in a Binary search tree, We need to understand the binary search tree. A Binary tree is a data structure in which each node can have at most two children. That is, each node in the binary tree will have data, left child and right child. The first node of the tree is called the Root.

How to find the maximum sum level in binary tree in Java? Example Tutorial

Hello guys, if you are preparing for a coding interview and wondering how to find the maximum sum level in a given binary tree in Java then you have come to the right place. I have been sharing binary tree coding problems for the last few months and in the past, we have seen questions like finding kth smallest element and finding the lowest common ancestor of a binary tree in Java in this article, you will learn how to find the maximum sum level in a given binary tree of integers or numbers. But, before finding the maximum sum level of a binary tree in java, we need to have a good understanding of a binary search tree. Both theoretical knowledge and how to implement binary search tree in Java is important to solve tree-based coding problems.

How to Find Lowest Common Ancestor of a Binary Tree in Java? Example Tutorial

Hello guys, if you are wondering how to find the lowest common ancestor of a binary tree in Java then you are at the right place. Earlier, I have shared 40+ binary tree questions and today I am going to share solution of one of the popular binary tree question here. To find the lowest common ancestor of a binary tree in java requires that we run through a binary search tree and how it operates. What then is a binary search tree? A Binary tree is a data structure in which each node can have at most two children. That is, each node in the binary tree will have data, left child and right child. The first node of the tree is called the Root.

How to get the first and last item in an array in Java? Example Tutorial

Firstly, before going about finding the first and the last item of an array in java. We need to fully understand what an array is and how it works. What then is an Array? An array is a data structure in java that holds values of the same type with its length specified right from creation time. Think of a container, like a crate of eggs or coke. What I am trying to say is that when you are creating your array, the items coming in must be the same as you have specified as length and you must specify how many items are coming. If you have stated that the items coming are integers, so it is and no other data type (e.g string, char e.t.c) can be there and vice versa. Or you can say an array is a collection of similar type of elements which has contiguous memory location.

Difference between array and Hashtable or HashMap in Java

A couple of days back someone asked me about the difference between an array and a hashtable, though this is a generic data structure and programming question, I'll answer it from both a general programming perspective as well on Java perspective where Hashtable is not just a data structure but also a class from Java Collection API. Even though both array and hashtable data structure are intended for fast search i.e. constant time search operation also known as O(1) search, the fundamental difference between them is that array require an index while hash table requires a key which could be another object.

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