PayPal Software Engineer interview questions

22 Software Engineers have shared notes from their PayPal interviews, with the questions they were asked in each round. That is 24% of the 91 PayPal interview notes on Screna AI.

22 Software Engineer interview notes

PayPal·Software Engineer·Technical Phone Screen

Jul 2026
PayPal software engineer interview with a deep dive into Java internals. The question felt more like a grad-school exam than a typical coding screen, which I wasn't fully prepared for.
  • Walk me through how HashMap works internally in Java, including the underlying data structures and how the implementation changed across different Java versions.
  • Beyond separate chaining, what other collision resolution strategies exist for hash maps, and what are the real trade-offs between them in terms of time complexity, memory usage, and cache performance?

“I knew the basics: array of buckets, linked list chaining, load factor.”

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PayPal·Software Engineer·Technical Phone Screen

Jul 2026
PayPal technical phone screen for a software engineer role, pretty deep on C++ internals. One question, but they really wanted you to know the details, not just the surface answer.
  • In C++, if you write `std::string a = "123"; std::string b = a;`, what operations are invoked under the hood? Walk through copy construction vs move semantics, how memory allocation typically works, Small String Optimization, and why the standard doesn't mandate copy-on-write.

“I knew the basics but stumbled a bit on SSO.”

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PayPal·Software Engineer·Technical Phone Screen

Jul 2026
Technical phone screen for a software engineer role at PayPal, focused pretty heavily on Java concurrency internals. One question, but it went deep fast.
  • What does the volatile keyword actually guarantee in Java's memory model? Walk through visibility, happens-before ordering, instruction reordering restrictions, and where volatile falls short compared to synchronized or locks.

“I started okay on visibility, said something about flushing to main memory and every thread reading fresh values.”

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PayPal·Software Engineer·Onsite - System Design / Architecture

Jun 2026
Did a system design round at PayPal for a software engineer role. The interviewer was pretty helpful with hints throughout, so it didn't feel like I was drowning the whole time.
  • Design a fraud detection service for a payment system.

“The interviewer dropped hints along the way which made it more of a conversation than an interrogation.”

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PayPal·Software Engineer·Technical Phone Screen

Jun 2026
Got a coding question from PayPal that looked clean on the surface but had enough edge cases to slow me down. Pretty standard technical screen format.
  • Given an encoded string in the format k[encoded_string] where the substring inside the brackets is repeated k times, write a function to decode it. Assume the input is always valid and digits only appear as repeat counts.

“I went straight for a stack-based approach and it mostly worked, but I fumbled on nested brackets for longer than I should have.”

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PayPal·Software Engineer·Technical Phone Screen

Jun 2026
PayPal coding screen, one question, pretty standard binary search territory. Nothing wild but the O(log n) constraint makes it clear they want you to actually think about complexity and not just brute force it.
  • Given a sorted array of distinct integers and a target value, return the index of the target if found. If not found, return the index where it would be inserted to keep the array sorted. Your solution must run in O(log n) time.

“Classic binary search but with a small twist at the end.”

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PayPal·Software Engineer·Technical Phone Screen

Jun 2026
PayPal technical phone screen for a software engineer role, pretty much a deep dive into Java concurrency. One question, but they really wanted you to go far with it.
  • Is Java's HashMap thread-safe? Walk through how ConcurrentHashMap achieves both thread safety and performance in modern JDKs, including things like lock striping, CAS operations, non-blocking reads, how it handles high collision scenarios, and its resizing behavior. When would you pick one over the other?

“Started fine.”

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PayPal·Software Engineer·Technical Phone Screen

Jun 2026
PayPal software engineering interview that went pretty deep into networking fundamentals. The TCP/UDP question felt like it had multiple layers and I wasn't sure how far they wanted me to go.
  • Compare TCP and UDP across reliability, ordering, congestion control, connection setup, and overhead. Then explain how TCP detects packet loss and triggers retransmission, covering timeouts, duplicate ACKs, fast retransmit, and selective acknowledgments.

“Started strong on the basic TCP vs UDP stuff, reliability and ordering are easy, but then they pushed into congestion control and I got a bit fuzzy.”

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PayPal·Software Engineer·Onsite - System Design / Architecture

Jun 2026
PayPal system design round for a software engineer role. One meaty question about cross-border payments that had a lot more moving parts than I expected going in.
  • Design a cross-border money transfer service like Remitly, accounting for country-specific transfer restrictions and real-time exchange rate lookups.

“I started with the happy path and got pretty far before they pushed on the compliance angle.”

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PayPal·Software Engineer·Technical Phone Screen

Jun 2026
PayPal software engineer interview with a graph/union-find problem that looks deceptively simple until you realize brute-force swapping won't cut it at scale.
  • Given a string and a list of index pairs where you can swap characters any number of times, return the lexicographically smallest string possible.

“My first instinct was to just simulate the swaps greedily and I wasted probably five minutes going down that path before realizing it doesn't work.”

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