PayPal Coding Interview Questions
25 PayPal coding interview problems with full optimal solutions — 16 easy, 6 medium, 3 hard. Every problem ships with multiple approaches (brute-force first, then the optimal), complexity tables for each, company-specific tips on what an PayPal interviewer values, and a FAQ section.
Showing 6 problems of 25
- #17mediumfrequently asked
17. Add Two Numbers
Add two non-negative integers represented as reversed linked lists and return the sum as a linked list. PayPal favors this problem because carry propagation mirrors real-world multi-precision arithmetic in payment processing systems.
- #18mediumfrequently asked
18. Longest Substring Without Repeating Characters
Find the length of the longest substring with all unique characters. PayPal uses this classic sliding-window problem to evaluate candidates' ability to maintain a dynamic window — directly analogous to deduplication windows in real-time transaction stream processing.
- #19mediumsometimes asked
19. Container With Most Water
Find two vertical lines that together with the x-axis form a container holding the most water. PayPal uses this two-pointer classic to test greedy reasoning and candidates' ability to prove why a pointer-shrink strategy is optimal — a proof skill valued in financial algorithm design.
- #20mediumfrequently asked
20. 3Sum
Find all unique triplets in an array that sum to zero. PayPal frequently asks this to test duplicate-skipping discipline and two-pointer mastery — skills that map to deduplication in reconciliation engines that match debits and credits across accounts.
- #21mediumsometimes asked
21. Group Anagrams
Group strings that are anagrams of each other into arrays. PayPal uses this hash-map grouping problem to evaluate key normalization skills — a pattern that appears in transaction deduplication and merchant category clustering in payment systems.
- #22mediumfrequently asked
22. Number of Islands
Count the number of islands (connected components of '1's) in a binary grid. PayPal uses this BFS/DFS grid traversal problem to test graph connectivity reasoning — directly applicable to fraud ring detection where connected transaction nodes form suspect clusters.
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