PayPal Software Engineer Interview Questions, Process, and Tips

Round duration - 60 minutes
Round difficulty - Medium

Technical interview round where the Interviewer asked me questions based on data structures and algorithms.

Q1. 
Design a Constant Time Data Structure
Create a data structure that maintains mappings between keys and values, supporting the following operations in constant time:
1. INSERT(key, value): Add or update t...read more
Ans. 
Design a constant time data structure for key-value mappings with operations like INSERT, DELETE, SEARCH, GET, GET_SIZE, and IS_EMPTY.
• Use a hash table to store key-value pairs for constant time operations.

• Implement INSERT by hashing the key and storing the value at the corresponding index.

• For DELETE, simply remove the key-value pair from the hash table.

• SEARCH can be done by checking if the key exists in the hash table.

• ...read more
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Q2. 
Integer to Roman Conversion
Given an integer N, convert it to its corresponding Roman numeral representation. Roman numerals comprise seven symbols: I, V, X, L, C, D, and M.
Example:
Input:
N = 2
Outp...read more
Ans. 
Convert an integer to its corresponding Roman numeral representation.
• Create a mapping of integer values to Roman numeral symbols

• Iterate through the mapping in descending order of values and build the Roman numeral representation

• Handle special cases like 4, 9, 40, 90, 400, 900 separately

• Repeat the process for each digit of the input integer
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Round duration - 60 minutes
Round difficulty - Medium

Technical interview round where the Interviewer asked me questions based on data structures and algorithms.

Q1. 
Total Area of Overlapping Rectangles Problem Statement
Determine the total area covered by two given rectangles on a 2-D coordinate plane, which may have an overlapping area.
Input:
The first line conta...read more
Ans. 
Calculate the total area covered by two overlapping rectangles on a 2-D coordinate plane.
• Parse input coordinates for two rectangles

• Calculate the area of each rectangle

• Find the overlapping area by determining the intersection of the rectangles

• Calculate the total area by adding the areas of both rectangles and subtracting the overlapping area
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Q2. 
Longest Repeating Subsequence Problem Statement
Given a string st, your task is to determine the length of the longest repeating subsequence such that no two subsequences have the same character at the sa...read more
Ans. 
The task is to find the length of the longest repeating subsequence in a string with no same characters at the same position.
• Iterate through the string and find the longest repeating subsequence by comparing characters at different positions.

• Use dynamic programming to keep track of the longest repeating subsequence found so far.

• Ensure that no two subsequences have the same character at the same position.

• Example: For in...read more
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Round duration - 60 minutes
Round difficulty - Medium

This was a system design round.

Q1. How would you design a rate limiter?
Ans. 
Rate limiter can be designed using token bucket algorithm to control the rate of requests.
• Use token bucket algorithm to control the rate of requests

• Set a limit on the number of requests allowed within a certain time frame

• Track the number of requests made and refill the bucket at a constant rate

• Reject requests that exceed the limit
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Round duration - 60 Minutes
Round difficulty - Easy

The interview was held in the evening on a weekday, Interview was nice and quite experienced, he asked me about my previous experience in the area and they told me about the team and work for which they were hiring, we did some discussion on that. Meanwhile, I was also asked a few questions on Database and SQL.

Q1. 
Find Magic Index in Sorted Array
Given a sorted array A consisting of N integers, your task is to find the magic index in the given array, where the magic index is defined as an index i such that A[i] = i...read more
Ans. 
Find the magic index in a sorted array where A[i] = i.
• Iterate through the array and check if A[i] = i for each index i

• Utilize binary search for a more efficient solution

• Handle cases where there are multiple magic indices or none at all
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Round duration - 60 minutes
Round difficulty - Medium

The interview was in the afternoon. There were some glitches with the teams meeting but it got sorted out in a few minutes. This round was purely coding based. He started with questions on arrays, linked lists, and string manipulation with an increasing level of hardness. The tricky part was that the online editor I was given for writing the code was not an IDE but a simple text editor, so I wasn't getting any help in terms of code completion or syntax errors or syntax highlighting.

Q1. 
Find All Pairs Adding Up to Target
Given an array of integers ARR of length N and an integer Target, your task is to return all pairs of elements such that they add up to the Target.
Input:
The first line ...read more
Ans. 
The task is to find all pairs of elements in an array that add up to a given target.
• Iterate through the array and for each element, check if the difference between the target and 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.
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