Must Do Coding Questions for Product Based Companies
Last Updated :
23 Jul, 2025
As the placement season is back, GeeksforGeeks is here to help you crack the interview. We have selected some most commonly asked and MUST DO practice problems to crack Product-based Company Interviews.
You can also take part in our mock placement contests which will help you learn different topics and practice at the same time, simulating the feeling of a real placement test environment.
Note: Now you can track your progress and learn from video editorials of these questions Complete Interview Preparation Course.
Math
| Question | Article | Practice |
|---|
| Missing Number in Array | Link | Link |
| Trailing Zeros in Factorial | Link | Link |
| A Simple Fraction | Link | Link |
| Nth Natural Number | Link | Link |
| Smallest Positive Integer that can not be represented as Sum | Link | Link |
Arrays
An array is a collection of items stored at contiguous memory locations. The idea is to store multiple items of the same type together.
Searching
| Question | Article | Practice |
|---|
| Search insert position of K in a sorted array | Link | Link |
| Collecting Wood | Link | Link |
| Left most and right most index | Link | Link |
| Bitonic Point | Link | Link |
| Search an element in sorted and rotated array | Link | Link |
| Square root of a number | Link | Link |
| Find missing in second array | Link | Link |
| Painter’s Partition Problem | Link | Link |
| Median of 2 sorted arrays of Different sizes | Link | Link |
| Allocate minimum number of pages | Link | Link |
Sorting
Matrix
A matrix represents a collection of numbers arranged in an order of rows and columns. It is necessary to enclose the elements of a matrix in parentheses or brackets.
String
Strings are defined as an array of characters. The difference between a character array and a string is the string is terminated with a special character ‘\0’.
| Question | Article | Practice |
|---|
| Reverse words in a given string | Link | Link |
| Longest Common Prefix | Link | Link |
| Roman Number to Integer | Link | Link |
| Next higher palindrome number using the same set of digits | Link | Link |
| Length of longest prefix suffix | Link | Link |
| Smallest window in string containing all characters | Link | Link |
| Validate an IP address | Link | Link |
| Implement Atoi | Link | Link |
| Look and say Pattern | Link | Link |
| Longest K unique characters substring | Link | Link |
Hashing
Bit Masking
Linked List
A linked list is a linear data structure, in which the elements are not stored at contiguous memory locations.
| Question | Article | Practice |
|---|
| Merge Two Sorted Linked Lists | Link | Link |
| Reverse a Linked List | Link | Link |
| Delete a Node without Head Pointer | Link | Link |
| Add two Numbers represented by linked lists | Link | Link |
| Finding middle element in a linked list | Link | Link |
| Check if linked list is palindrome | Link | Link |
| Rearrange a linked list | Link | Link |
| Detect and Remove a loop In Linked List | Link | Link |
| Merge Sort for Linked List | Link | Link |
| Intersection of Linked List | Link | Link |
| Rotate Linked List by K places | Link | Link |
| Flattening a Linked List | Link | Link |
| Reverse a linked list in groups of given size | Link | Link |
| Partition a linked list around a given value | Link | Link |
| Clone a linked list with next and random pointers | Link | Link |
Stack
A stack is a linear data structure in which elements can be inserted and deleted only from one side of the list, called the top. A stack follows the LIFO (Last In First Out) principle.
Queue
A queue is a linear data structure in which elements can be inserted only from one side of the list called rear, and the elements can be deleted only from the other side called the front. The queue data structure follows the FIFO (First In First Out) principle.
| Question | Article | Practice |
|---|
| Maximum of all subarrays of size K | Link | Link |
| Circular tour (Sliding Window) | Link | Link |
Heap
A Heap is a special Tree-based data structure in which the tree is a complete binary tree.
Binary Tree
A tree whose elements have at most 2 children is called a binary tree. Since each element in a binary tree can have only 2 children, we typically name them the left and right child.
Binary Search Tree
Binary Search Tree is a node-based binary tree data structure which has the following properties:
- The left subtree of a node contains only nodes with keys lesser than the node’s key.
- The right subtree of a node contains only nodes with keys greater than the node’s key.
- The left and right subtree each must also be a binary search tree.
Graph
A Graph is a non-linear data structure consisting of nodes and edges. The nodes are sometimes also referred to as vertices and the edges are lines or arcs that connect any two nodes in the graph.
Trie
Trie is an efficient information retrieval data structure. Using Trie, search complexities can be brought to optimal limit (key length).
Greedy
Greedy is an algorithmic paradigm that builds up a solution piece by piece, always choosing the next piece that offers the most obvious and immediate benefit.
DP
Dynamic Programming is mainly an optimization over plain recursion. Wherever we see a recursive solution that has repeated calls for same inputs, we can optimize it using Dynamic Programming.
Recursion
The process in which a function calls itself directly or indirectly is called recursion and the corresponding function is called as recursive function.
Backtracking
Backtracking is an algorithmic-technique for solving problems recursively by trying to build a solution incrementally, one piece at a time, removing those solutions that fail to satisfy the constraints of the problem at any point of time (by time, here, is referred to the time elapsed till reaching any level of the search tree).
Algorithms
Design
You may also check our
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Note:
To complement your practice of these essential coding questions, consider enrolling in the DSA to Development - Coding Guide course offered by GeeksforGeeks. This course provides a structured approach to mastering data structures, algorithms, and key coding concepts, ensuring you're well-prepared for interviews at top product-based companies. With a blend of theory and practical exercises, this course can help you build the skills needed to tackle any interview with confidence. Explore the course to take your preparation to the next level.
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Basics & Prerequisites
Data Structures
Getting Started with Array Data StructureArray is a collection of items of the same variable type that are stored at contiguous memory locations. It is one of the most popular and simple data structures used in programming. Basic terminologies of ArrayArray Index: In an array, elements are identified by their indexes. Array index starts fr
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String in Data StructureA string is a sequence of characters. The following facts make string an interesting data structure.Small set of elements. Unlike normal array, strings typically have smaller set of items. For example, lowercase English alphabet has only 26 characters. ASCII has only 256 characters.Strings are immut
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Hashing in Data StructureHashing is a technique used in data structures that efficiently stores and retrieves data in a way that allows for quick access. Hashing involves mapping data to a specific index in a hash table (an array of items) using a hash function. It enables fast retrieval of information based on its key. The
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Linked List Data StructureA linked list is a fundamental data structure in computer science. It mainly allows efficient insertion and deletion operations compared to arrays. Like arrays, it is also used to implement other data structures like stack, queue and deque. Here’s the comparison of Linked List vs Arrays Linked List:
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Stack Data StructureA Stack is a linear data structure that follows a particular order in which the operations are performed. The order may be LIFO(Last In First Out) or FILO(First In Last Out). LIFO implies that the element that is inserted last, comes out first and FILO implies that the element that is inserted first
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Queue Data StructureA Queue Data Structure is a fundamental concept in computer science used for storing and managing data in a specific order. It follows the principle of "First in, First out" (FIFO), where the first element added to the queue is the first one to be removed. It is used as a buffer in computer systems
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Tree Data StructureTree Data Structure is a non-linear data structure in which a collection of elements known as nodes are connected to each other via edges such that there exists exactly one path between any two nodes. Types of TreeBinary Tree : Every node has at most two childrenTernary Tree : Every node has at most
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Graph Data StructureGraph Data Structure is a collection of nodes connected by edges. It's used to represent relationships between different entities. If you are looking for topic-wise list of problems on different topics like DFS, BFS, Topological Sort, Shortest Path, etc., please refer to Graph Algorithms. Basics of
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Trie Data StructureThe Trie data structure is a tree-like structure used for storing a dynamic set of strings. It allows for efficient retrieval and storage of keys, making it highly effective in handling large datasets. Trie supports operations such as insertion, search, deletion of keys, and prefix searches. In this
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Algorithms
Searching AlgorithmsSearching algorithms are essential tools in computer science used to locate specific items within a collection of data. In this tutorial, we are mainly going to focus upon searching in an array. When we search an item in an array, there are two most common algorithms used based on the type of input
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Sorting AlgorithmsA Sorting Algorithm is used to rearrange a given array or list of elements in an order. For example, a given array [10, 20, 5, 2] becomes [2, 5, 10, 20] after sorting in increasing order and becomes [20, 10, 5, 2] after sorting in decreasing order. There exist different sorting algorithms for differ
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Introduction to RecursionThe process in which a function calls itself directly or indirectly is called recursion and the corresponding function is called a recursive function. A recursive algorithm takes one step toward solution and then recursively call itself to further move. The algorithm stops once we reach the solution
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Greedy AlgorithmsGreedy algorithms are a class of algorithms that make locally optimal choices at each step with the hope of finding a global optimum solution. At every step of the algorithm, we make a choice that looks the best at the moment. To make the choice, we sometimes sort the array so that we can always get
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Graph AlgorithmsGraph is a non-linear data structure like tree data structure. The limitation of tree is, it can only represent hierarchical data. For situations where nodes or vertices are randomly connected with each other other, we use Graph. Example situations where we use graph data structure are, a social net
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Dynamic Programming or DPDynamic Programming is an algorithmic technique with the following properties.It is mainly an optimization over plain recursion. Wherever we see a recursive solution that has repeated calls for the same inputs, we can optimize it using Dynamic Programming. The idea is to simply store the results of
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Bitwise AlgorithmsBitwise algorithms in Data Structures and Algorithms (DSA) involve manipulating individual bits of binary representations of numbers to perform operations efficiently. These algorithms utilize bitwise operators like AND, OR, XOR, NOT, Left Shift, and Right Shift.BasicsIntroduction to Bitwise Algorit
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Advanced
Segment TreeSegment Tree is a data structure that allows efficient querying and updating of intervals or segments of an array. It is particularly useful for problems involving range queries, such as finding the sum, minimum, maximum, or any other operation over a specific range of elements in an array. The tree
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Pattern SearchingPattern searching algorithms are essential tools in computer science and data processing. These algorithms are designed to efficiently find a particular pattern within a larger set of data. Patten SearchingImportant Pattern Searching Algorithms:Naive String Matching : A Simple Algorithm that works i
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GeometryGeometry is a branch of mathematics that studies the properties, measurements, and relationships of points, lines, angles, surfaces, and solids. From basic lines and angles to complex structures, it helps us understand the world around us.Geometry for Students and BeginnersThis section covers key br
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