20+ PayPal Software Developer Interview Questions and Answers

Find the maximum sum that can be obtained from a path in a matrix from the first row to the last row.

• Use dynamic programming to keep track of the maximum sum at each cell in the matrix.

• Start from the second row and update each cell with the maximum sum from the cell above and diagonally above left or right.

• The maximum sum at the last row will be the answer for each test case.

Implement counting sort algorithm to sort an array of integers without comparisons.

• Count the frequency of each element in the input array.

• Calculate the prefix sum of frequencies to determine the position of each element in the sorted array.

• Place each element in its correct position based on the prefix sum.

• Time complexity of counting sort is O(n+k), where n is the number of elements and k is the range of input.

• Example: Input: ARR = {-2, 1, 2, -1, 0}, Output: {-2, -1, 0, 1, 2}

Find K largest elements in an unsorted array and return them in non-decreasing order.

• Sort the array in non-decreasing order.

• Return the last K elements of the sorted array.

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 in a pair.

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

Find the Kth largest element in an array of distinct positive integers.

• Sort the array in non-increasing order and return the Kth element.

• Handle multiple test cases efficiently.

• Ensure all elements in the array are distinct.

Generate all possible combinations of balanced parentheses for a given number of pairs.

• Use backtracking to generate all possible combinations of balanced parentheses.

• Keep track of the number of open and close parentheses used in each combination.

• Recursively generate combinations by adding open parentheses if there are remaining, and closing parentheses if the number of open parentheses is greater than the number of close parentheses.

• Return the list of valid combinations as an...read more

The problem involves finding the minimum sum path from a specified cell to the top left corner of a matrix.

• Start from the specified cell and calculate the minimum sum path to reach the top left corner using dynamic programming.

• Consider the three possible moves: down, right, and down-right diagonal.

• Keep track of the minimum sum at each cell and update it based on the minimum of the three possible moves.

• Finally, the minimum sum at the top left corner will be the answer.

Given an array of positive integers and an integer K, determine if there exists a subset whose sum equals K.

• Use dynamic programming to solve this problem efficiently

• Create a 2D array to store if a subset with a particular sum exists

• Iterate through the array and update the 2D array accordingly

• Check if the value at the end of the iteration is true for the given K

Check if given strings with parentheses are balanced or not.

• Use a stack to keep track of opening parentheses

• Iterate through the string and push opening parentheses onto the stack

• When a closing parenthesis is encountered, pop from the stack and check if it matches the closing parenthesis

• If stack is empty at the end and all parentheses are matched, the string is balanced

Implement a function to delete a node from a linked list at a specified position.

• Traverse the linked list to find the node at the specified position.

• Update the pointers of the previous and next nodes to skip the node to be deleted.

• Handle edge cases such as deleting the head or tail of the linked list.

• Ensure to free the memory of the deleted node to avoid memory leaks.

BFS traversal in a disconnected graph starting from vertex 0.

• Implement BFS algorithm to traverse the graph starting from vertex 0.

• Use a queue to keep track of visited nodes and their neighbors.

• Ensure to print the traversal sequence in the correct order.

• Handle disconnected components by checking for unvisited nodes.

• Follow the BFS approach of exploring neighbors before moving to the next level.

Replace spaces in a string with '@40'.

• Iterate through each character in the string

• Replace spaces with '@40'

• Return the modified string

Create a program to count lowercase alphabets, digits, and white spaces from user input until '$' is encountered.

• Read characters from input stream until '$' is encountered

• Count lowercase alphabets, digits, and white spaces separately

• Print the counts of each character type as three integers separated by spaces

To check internet connection on a system, you can use various methods like pinging a website or checking network status.

• Use ping command to check connectivity to a website (e.g. ping www.google.com)

• Check network status using network settings or command line tools

• Try accessing a website or online service to verify internet connection

The Fibonacci series has applications in various fields such as mathematics, computer science, art, and nature.

• Used in algorithms for optimization problems and dynamic programming.

• Found in nature, such as the arrangement of leaves on a stem, the branching of trees, and the spiral shapes of shells.

• Applied in financial markets for predicting stock prices and analyzing market trends.

• Utilized in art and design for creating visually appealing patterns and compositions.

You can find a defective ball among 10 given balls in 2 attempts using a two-pan balance scale.

• Divide the 10 balls into two groups of 5 each.

• Weigh the two groups on the balance scale.

• If one group is heavier, it contains the defective ball. If they are equal, the defective ball is in the remaining 5 balls.

• Divide the group of 5 balls with the defective one into two groups of 2 and 3 balls.

• Weigh the two groups on the balance scale.

• If one group is heavier, it contains the defecti...read more

Object Oriented Programming is a programming paradigm that uses objects to represent real-world entities.

• Encapsulation: bundling data and methods that operate on that data within one unit

• Inheritance: creating new classes from existing ones, inheriting their properties and methods

• Polymorphism: ability of objects to take on multiple forms or behaviors

• Abstraction: hiding complex implementation details and providing a simplified interface

• Example: A car object can have properties ...read more

When you type a URL in a web browser, the browser sends a request to the server hosting the website, which then responds with the necessary files to display the webpage.

• Browser checks cache for DNS resolution

• If not found, browser sends a DNS query to resolve the domain name to an IP address

• Browser establishes a TCP connection with the server

• Browser sends an HTTP request to the server for the webpage

• Server processes the request and sends back the necessary files (HTML, CSS, JS...read more

Find subset of numbers in array that sum up to zero.

• Use a nested loop to iterate through all possible subsets.

• Calculate the sum of each subset and check if it equals zero.

• Store the subset if the sum is zero.

• Optimize the solution by using a hash set to store the cumulative sum of elements.

OOP is a programming paradigm based on the concept of objects, which can contain data in the form of fields and code in the form of procedures.

• OOP focuses on creating objects that interact with each other to solve problems.

• Key concepts include encapsulation, inheritance, and polymorphism.

• Encapsulation involves bundling data and methods that operate on the data into a single unit.

• Inheritance allows classes to inherit attributes and methods from other classes.

• Polymorphism enabl...read more

Abstraction is hiding implementation details while polymorphism is using a single interface for multiple types.

• Abstraction: Encapsulation, Interfaces, Abstract classes

• Polymorphism: Method Overloading, Method Overriding, Interfaces

• Abstraction Example: Car - we don't need to know how the engine works to drive it

• Polymorphism Example: Animal - different animals have different sounds but they all have a 'makeSound' method

SQL query to find the nth highest salary

• Use the ORDER BY clause to sort salaries in descending order

• Use the LIMIT and OFFSET clauses to skip the first n-1 highest salaries

• Combine the above steps in a single query to find the nth highest salary

Design a Cinema Ticket Reservation System

• Use a database to store movie information, showtimes, and seat availability

• Allow users to search for movies, select showtimes, and choose seats

• Implement a payment system for ticket purchases

• Send confirmation emails with QR codes for ticket validation

PayPal is an online payment system that allows individuals and businesses to transfer funds electronically.

• Allows users to make payments and money transfers online

• Offers a secure and convenient way to pay for goods and services

• Provides a platform for businesses to accept payments online

• Offers buyer and seller protection for eligible transactions

• Can be used to send and receive money internationally

BFS (Breadth-First Search) is a graph traversal algorithm that explores all the vertices of a graph in breadth-first order.

• BFS starts at a given vertex and explores all its neighbors before moving to the next level of vertices.

• It uses a queue data structure to keep track of the vertices to be visited.

• BFS guarantees that it visits all the vertices of a connected graph.

• It can be used to find the shortest path between two vertices in an unweighted graph.

Virtual functions are functions in a base class that are overridden in derived classes to achieve runtime polymorphism.

• Virtual functions are declared in a base class with the 'virtual' keyword.

• They are overridden in derived classes using the 'override' keyword.

• They allow a function to be called based on the runtime type of an object.

• Virtual functions enable dynamic binding and late binding in C++.

• Example: virtual void display() = 0; in base class and void display() override {...read more