PayPal Backend Developer Interview Questions and Answers

Minimum cost to reach last cell of 2D matrix with only downward or right moves.

• Use dynamic programming approach to solve the problem.

• Calculate minimum cost for each cell by considering minimum cost of its adjacent cells.

• Final answer will be the minimum cost to reach the last cell.

Design a stack that supports getMin functionality to return the minimum element in the stack.

• Create two stacks, one for storing the actual elements and another for storing the minimum elements.

• Push elements onto both stacks simultaneously.

• When popping an element, pop from both stacks.

• To get the minimum element, peek at the top of the minimum stack.

TreeSet is a data structure that stores unique elements in sorted order.

• TreeSet is implemented using a Red-Black tree

• It provides O(log n) time complexity for basic operations like add, remove, and contains

• It also provides methods like first(), last(), headSet(), tailSet(), and subSet()

• TreeSet can be used to implement priority queues and sorting algorithms

Design an ArrayList with getMax functionality.

• Create a custom ArrayList class that extends the existing ArrayList class.

• Add a getMax() method that returns the maximum value in the list.

• Override the add() method to keep track of the maximum value in the list.

• Update the maximum value whenever an element is added or removed from the list.

SOLID principles are a set of five design principles for writing maintainable and scalable code.

• S - Single Responsibility Principle

• O - Open/Closed Principle

• L - Liskov Substitution Principle

• I - Interface Segregation Principle

• D - Dependency Inversion Principle

HashSet is a collection that stores unique elements by using a hash table.

• Elements are stored based on their hash code

• Uses hashCode() and equals() methods to check for duplicates

• Does not maintain insertion order

• Allows null values

• Example: HashSet set = new HashSet<>(); set.add("apple"); set.add("banana");