PayPal Coding Interview Questions

Showing 9 problems of 25

• #1easyfrequently asked

  1. Two Sum

  Given an array of integers and a target, return indices of the two numbers that add up to the target. PayPal asks this to gauge whether you reach for a hash map immediately — the same reflex they want when you're matching a payment to a pending invoice by amount.

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• #2easyfrequently asked

  2. Valid Parentheses

  Given a string of brackets, decide whether they are balanced. PayPal asks this as a stack-comfort warm-up — the same data structure that powers their transaction-state-machine stack for rollback on failed payments.

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• #3easyfrequently asked

  3. Merge Two Sorted Lists

  Merge two sorted linked lists into one sorted list by splicing nodes together. PayPal asks this as a warm-up to gauge pointer comfort — the same primitive they use when merging two sorted streams of authorized and captured payments by timestamp.

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• #12easyfrequently asked

  12. Maximum Depth of Binary Tree

  Find the maximum depth of a binary tree. PayPal uses this as a recursion litmus — the same primitive they use to measure the depth of a chain of related transactions when investigating circular fraud rings.

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• #15easyfrequently asked

  15. Best Time to Buy and Sell Stock

  Find the maximum profit from a single buy-sell transaction in a price array. PayPal treats this as a core financial-reasoning problem — interviewers look for candidates who can frame it as tracking running minimum and maximum gain.

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• #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.

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• #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.

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• #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.

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• #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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