50+ Doolally Interview Questions and Answers

The problem involves finding the maximum number of apples Alice can collect in a grid while following specific rules.

• Create a recursive function to explore all possible paths from the starting point to the ending point while keeping track of the collected apples.

• Consider the constraints and optimize the solution to avoid unnecessary computations.

• Use dynamic programming to store and reuse the results of subproblems to improve efficiency.

• Ensure to handle cases where there is no...read more

Find the minimum number of dice throws required to reach the last cell on a 'Snake and Ladder' board.

• Start from the bottom left cell and move according to dice outcomes (1-6).

• Utilize snakes and ladders to reach the last cell faster.

• Keep track of the minimum number of throws required to reach the last cell.

• If unreachable, return -1 as output.

Implement a Stack data structure using a Singly Linked List with operations in O(1) time.

• Create a class named Stack with getSize, isEmpty, push, pop, and getTop methods.

• Use a Singly Linked List to store the elements of the stack.

• Ensure each operation runs in constant time complexity.

• Handle edge cases like empty stack appropriately.

• Example: If input is '5 3 10 5 1 2 4', the output should be '10 1 false'.

Detect if a singly linked list forms a cycle by checking if a node's next points back to a previous node.

• Use Floyd's Tortoise and Hare algorithm to detect a cycle in the linked list.

• Initialize two pointers, slow and fast, and move them at different speeds to detect a cycle.

• If there is a cycle, the fast pointer will eventually catch up to the slow pointer.

• If the fast pointer reaches the end of the list (null), there is no cycle.

Find the position of the lone '1' bit in the binary representation of a given non-negative integer.

• Iterate through the bits of the integer to find the position of the lone '1'.

• Use bitwise operations to check if there is exactly one '1' bit in the binary representation.

• Return the position of the lone '1' or -1 if there isn't exactly one '1'.

Find the node where two linked lists merge, return -1 if no merging occurs.

• Traverse both lists to find their lengths and the difference in lengths

• Move the pointer of the longer list by the difference in lengths

• Traverse both lists simultaneously until they meet at the merging point

Given an array of integers and a target, find all pairs of elements that add up to the target.

• Iterate through the array and for each element, check if the target minus the element exists in a hash set.

• If it exists, add the pair to the result. If not, add the element to the hash set.

• Handle cases where the same element is used twice to form a pair.

• Return (-1, -1) if no pair is found.

Given a list of strings, determine if a target string can be formed by combining one or more strings from the list.

• Iterate through all possible combinations of strings from the list to check if they form the target string.

• Use recursion to try different combinations of strings.

• Optimize the solution by using memoization to store intermediate results.

• Handle edge cases like empty input or target string.

The task is to find the total number of ways to make change for a specified value using given denominations.

• Use dynamic programming to solve this problem efficiently.

• Create a 1D array to store the number of ways to make change for each value from 0 to the target value.

• Iterate through the denominations and update the array based on the current denomination.

• The final answer will be the value at the target index of the array.

Add two numbers represented as linked lists in reverse order and return the sum as a linked list.

• Traverse both linked lists simultaneously while keeping track of carry.

• Create a new linked list to store the sum digits.

• Handle cases where one list is longer than the other or there is a final carry.

• Remember to reverse the final linked list before returning the head.

Check if two strings are anagrams of each other by comparing their sorted characters.

• Sort the characters of both strings and compare them.

• Use a dictionary to count the frequency of characters in each string and compare the dictionaries.

• Ensure both strings have the same length before proceeding with comparison.

• Example: For input 'spar' and 'rasp', after sorting both strings, they become 'aprs' which are equal, so return True.

Find the maximum path sum between two leaf nodes in a binary tree.

• Traverse the tree to find the maximum path sum between two leaf nodes

• Consider both cases where the path passes through the root and where it doesn't

• Keep track of the maximum sum while traversing the tree

Design a Least Recently Used (LRU) cache data structure that supports get and put operations with capacity constraint.

• Implement a doubly linked list to maintain the order of recently used keys.

• Use a hashmap to store key-value pairs for quick access.

• When capacity is reached, evict the least recently used item before inserting a new item.

• Update the position of a key in the linked list whenever it is accessed or updated.

• Handle get and put operations efficiently to maintain the L...read more

Find all possible paths for a rat in a maze to reach its destination.

• Use backtracking to explore all possible paths in the maze.

• Mark visited cells and backtrack when reaching dead ends.

• Print the path when reaching the destination cell.

• Consider all possible movements: left, right, up, and down.

• Ensure the rat can only move through cells marked as 1.

Implement a function to return the spiral order traversal of a binary tree.

• Traverse the binary tree in a spiral order, alternating between left to right and right to left at each level

• Use a queue to keep track of nodes at each level and a flag to switch direction

• Return the list of nodes in spiral order traversal

Return the level order traversal of a binary tree given in level order with null nodes represented by -1.

• Create a queue to store nodes for level order traversal

• Start with the root node, enqueue it, then dequeue and print its value, enqueue its children, repeat until queue is empty

• Handle null nodes represented by -1 by skipping them during traversal

Find the length of the longest substring without repeating characters in a given string.

• Use a sliding window approach to keep track of the longest substring without repeating characters.

• Use a hashmap to store the index of each character as it appears in the string.

• Update the start index of the window when a repeating character is found.

• Calculate the maximum length of the window as you iterate through the string.

• Return the maximum length as the result.

Find the length of the longest contiguous subarray that sums to zero in an array of integers.

• Use a hashmap to store the cumulative sum and its corresponding index.

• Iterate through the array, updating the sum and checking if the current sum exists in the hashmap.

• If the sum exists in the hashmap, update the maximum length of subarray with sum zero.

• Return the maximum length of subarray with sum zero.

Detect and remove loop in a singly linked list in place with O(n) time complexity and O(1) space complexity.

• Use Floyd's Cycle Detection Algorithm to identify the loop in the linked list.

• Once the loop is detected, use two pointers to find the start of the loop.

• Adjust the pointers to remove the loop and return the modified linked list.

Use two wires of different lengths to measure a specific amount of time by burning them simultaneously.

• Burn both wires at the same time, one wire will finish burning before the other

• Measure the time it takes for the first wire to burn completely

• Use this time as a reference to measure the specific amount of time by burning the second wire

An IP address is a unique numerical label assigned to each device connected to a computer network, typically represented by 32 bits.

• An IP address is used to identify and locate devices on a network.

• It consists of four sets of numbers separated by periods, such as 192.168.1.1.

• IPv4 addresses are 32 bits long, while IPv6 addresses are 128 bits long.

A router is a networking device that forwards data packets between computer networks. It differs from a gateway in terms of functionality and scope.

• A router operates at the network layer of the OSI model, making decisions based on IP addresses.

• Routers connect multiple networks together and determine the best path for data to travel.

• Gateways, on the other hand, translate between different types of networks or protocols.

• Gateways operate at the application layer of the OSI model...read more

MAC addresses are necessary for local network communication and are used to uniquely identify devices on a network.

• MAC addresses are used at the data link layer of the OSI model to identify devices within the same local network.

• IP addresses are used at the network layer to identify devices across different networks.

• MAC addresses are hardcoded into network interface cards (NICs) and are used for communication within the same network segment.

• MAC addresses are essential for Ethe...read more

Friend class and function in OOP allows specific classes or functions to access private and protected members of a class.

• Friend class/function can access private and protected members of a class without violating encapsulation.

• It allows for selective sharing of data between classes without exposing all members to the outside world.

• Friendship is not mutual - a class can declare another class as a friend, but the other class does not automatically become a friend.

• Example: In a ...read more

To measure exactly 4 liters of water, fill the 3-liter can, pour it into the 5-liter can, refill the 3-liter can, pour enough to fill the 5-liter can, leaving 1 liter in the 3-liter can, then empty the 5-liter can and pour the remaining 1 liter from the 3-liter can into the 5-liter can, finally refill the 3-liter can and pour it into the 5-liter can to get exactly 4 liters.

• Fill the 3-liter can and pour it into the 5-liter can.

• Refill the 3-liter can and pour enough to fill the...read more

Object Oriented Programming concepts include encapsulation, inheritance, polymorphism, and abstraction.

• Encapsulation: Bundling data and methods that operate on the data into a single unit (class). Example: Class Car with properties like color and methods like drive().

• Inheritance: Creating new classes based on existing classes, inheriting their attributes and methods. Example: Class SUV inheriting from class Car.

• Polymorphism: Objects of different classes can be treated as obje...read more

ArrayList is implemented using a dynamic array while LinkedList is implemented using a doubly linked list.

• ArrayList provides fast random access but slow insertion and deletion operations.

• LinkedList provides fast insertion and deletion operations but slow random access.

• Example: ArrayList is suitable for scenarios where frequent access and traversal of elements is required, while LinkedList is suitable for scenarios where frequent insertion and deletion of elements is required.

Abstraction focuses on hiding implementation details, while inheritance allows a class to inherit properties and behavior from another class.

• Abstraction is the concept of hiding the complex implementation details and showing only the necessary features of an object.

• Inheritance is a mechanism where a new class inherits properties and behavior from an existing class.

• Abstraction is achieved through interfaces and abstract classes, while inheritance is implemented using the 'exte...read more

Different types of semaphores include binary semaphores, counting semaphores, and mutex semaphores.

• Binary semaphores: Can only have two states - 0 or 1. Used for mutual exclusion.

• Counting semaphores: Can have multiple states. Used for synchronization among multiple processes.

• Mutex semaphores: Similar to binary semaphores but with additional features like priority inheritance and deletion safety.

The OSI Reference Model is a conceptual framework that standardizes the functions of a telecommunication or computing system into seven layers.

• The OSI Reference Model stands for Open Systems Interconnection Reference Model.

• It consists of seven layers: Physical, Data Link, Network, Transport, Session, Presentation, and Application.

• Each layer has specific functions and communicates with the adjacent layers.

• The model helps in understanding how different networking protocols work...read more

Memory protection in operating systems is a mechanism to prevent a process from accessing memory that has not been allocated to it.

• Memory protection prevents a process from accessing memory locations outside its allocated space.

• It helps in preventing one process from interfering with the memory of another process.

• Operating systems use techniques like virtual memory and access control lists to implement memory protection.

• Examples include segmentation fault in Unix systems when...read more

IPv6 has a larger address space, improved security features, and better support for mobile devices compared to IPv4.

• IPv4 uses 32-bit addresses while IPv6 uses 128-bit addresses.

• IPv4 supports around 4.3 billion unique addresses, whereas IPv6 supports 340 undecillion unique addresses.

• IPv6 has built-in security features like IPsec, while IPv4 requires additional security protocols.

• IPv6 has better support for mobile devices and IoT devices due to its larger address space and impr...read more

During system boot, the BIOS performs Power-On Self Test (POST), loads the operating system, and initializes hardware components.

• BIOS (Basic Input/Output System) performs Power-On Self Test (POST) to check hardware components

• BIOS loads the bootloader from the boot device (e.g. hard drive, SSD)

• Bootloader loads the operating system kernel into memory

• Operating system initializes hardware components and starts system services

• User login prompt is displayed for user interaction

Thrashing in operating systems is a situation where the system is spending more time swapping data between memory and disk than actually executing tasks.

• Occurs when the system is overwhelmed with too many processes competing for limited resources

• Results in a decrease in overall system performance

• Can be alleviated by optimizing memory usage or adding more physical memory

• Example: A system with insufficient RAM running multiple memory-intensive applications

A static member in C++ is a member of a class that is shared among all instances of the class.

• Static members are declared using the 'static' keyword.

• They are not associated with any specific instance of the class, but rather with the class itself.

• They can be accessed using the scope resolution operator '::'.

• Static members are commonly used for constants, utility functions, or shared data among all instances of a class.

C++ supports polymorphism through virtual functions and inheritance.

• C++ supports polymorphism through virtual functions and inheritance

• Virtual functions allow a function to be overridden in a derived class

• Base class pointers can point to derived class objects, enabling polymorphic behavior

• Example: class Animal { virtual void makeSound() { cout << 'Animal sound'; } }; class Dog : public Animal { void makeSound() { cout << 'Bark'; } };

• Example: Animal* a = new Dog(); a->makeSoun...read more

Looping statements are used to execute a block of code repeatedly. Branching statements alter the flow of control in a program.

• Looping statements are used when we want to execute a block of code repeatedly until a certain condition is met.

• Examples of looping statements include for, while, and do-while loops.

• Branching statements are used to alter the normal flow of control in a program.

• Examples of branching statements include if-else statements, switch statements, and the brea...read more

Piping in Unix/Linux allows the output of one command to be used as the input for another command.

• Piping is done using the | symbol

• Multiple commands can be piped together

• Piping allows for the creation of complex command chains

• Example: ls -l | grep txt

A static variable in C is a variable that retains its value between function calls.

• Static variables are declared using the 'static' keyword.

• They are initialized only once and retain their value throughout the program's execution.

• Static variables have a default value of 0 if not explicitly initialized.

• They are stored in the data segment of the program's memory.

• Example: static int count = 0; declares a static variable 'count' with an initial value of 0.

DNS stands for Domain Name System, which translates domain names to IP addresses.

• DNS is like a phone book for the internet, translating human-readable domain names (like google.com) to IP addresses (like 172.217.3.206).

• It helps users access websites by typing in easy-to-remember domain names instead of complex IP addresses.

• DNS servers store records of domain names and their corresponding IP addresses, allowing for efficient and quick lookups.

• DNS also plays a role in email del...read more

A namespace in C++ is a declarative region that provides a scope for the identifiers within it.

• Namespaces help in organizing code by grouping related classes, functions, and variables.

• They prevent naming conflicts by allowing the same name to be used in different namespaces.

• Example: namespace myNamespace { int x; }

• Example: using namespace std; // for using standard library functions without prefix

Priority inversion is a scenario in scheduling where a lower priority task holds a resource needed by a higher priority task, causing the higher priority task to wait.

• Occurs when a low priority task locks a resource needed by a high priority task

• Results in the high priority task being blocked and unable to proceed

• Can lead to delays in critical tasks and impact system performance

• Commonly addressed through priority inheritance or priority ceiling protocols

ARP stands for Address Resolution Protocol, used to map IP addresses to MAC addresses in a local network.

• ARP is used to find the MAC address of a device based on its IP address

• It operates at the data link layer of the OSI model

• ARP requests are broadcasted to all devices on the local network

• Example: When a device wants to communicate with another device on the same network, it uses ARP to find the MAC address of the destination device

Python is a high-level, interpreted programming language known for its simplicity and readability.

• Python is used for web development, data analysis, artificial intelligence, and more.

• It uses if statements for conditional execution of code.

• Example: if x > 5: print('x is greater than 5')

• Python also supports elif and else statements for more complex conditions.

Program to convert 24hr input into AM-PM formatted output

• Create a function that takes a 24-hour time input as a string

• Use the datetime module in Python to convert the input to a datetime object

• Format the datetime object to display in AM-PM format

• Return the formatted time as a string

Two sum problem involves finding two numbers in an array that add up to a specific target.

• Brute force approach involves nested loops to check all possible pairs of numbers.

• Optimal approach uses a hashmap to store the difference between target and current number.

• Example: nums = [2, 7, 11, 15], target = 9. Optimal solution: [0, 1] (2 + 7 = 9).

Object-oriented programming concepts that focus on objects and classes for code organization and reusability.

• Encapsulation: bundling data and methods that operate on the data into a single unit (class)

• Inheritance: ability of a class to inherit properties and behavior from another class

• Polymorphism: ability to present the same interface for different data types

Find the longest subarray with sum 0 in an array of integers.

• Use a hash table to store the sum and its index.

• Iterate through the array and calculate the cumulative sum.

• If the cumulative sum is already in the hash table, then the subarray between the current index and the index in the hash table has a sum of 0.

• Keep track of the longest subarray with sum 0 seen so far.

• Return the length of the longest subarray with sum 0.

LRU cache is a data structure that stores the most recently used items, discarding the least recently used items when full.

• Use a doubly linked list to keep track of the order of items based on their usage.

• Use a hashmap to quickly access items in the cache.

• When a new item is accessed, move it to the front of the linked list and update the hashmap.

• When the cache is full, remove the least recently used item from the end of the linked list and the hashmap.