PayPal Coding Interview Questions

Showing 16 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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• #4easysometimes asked

  4. Remove Duplicates from Sorted Array

  Remove duplicates from a sorted array in-place and return the new length. PayPal asks this to test the two-pointer reflex — the same technique they apply when deduplicating idempotency keys in a sorted append-only ledger.

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• #5easysometimes asked

  5. Remove Element

  Remove all occurrences of a value from an array in-place and return the new length. PayPal uses this to test the same two-pointer reflex they need when filtering reversed transactions out of a daily settlement batch.

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• #6easysometimes asked

  6. Search Insert Position

  Given a sorted array and a target, return the index where target is found, or where it would be inserted to keep the array sorted. PayPal asks this to test whether you can write a bug-free binary search — the foundation for fast lookups in their sorted fraud-rule index.

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• #7easysometimes asked

  7. Plus One

  Given a non-empty array of digits representing a large integer, increment it by one. PayPal asks this to test arbitrary-precision arithmetic awareness — currency amounts at scale exceed 64-bit, and you cannot lose a cent to overflow.

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• #8easysometimes asked

  8. Merge Sorted Array

  Merge two sorted arrays in-place into the first one (which has buffer space at the end). PayPal asks this to test reverse-pointer thinking — the same approach they use when interleaving an authorized-transactions buffer with a capture-events buffer for end-of-day reconciliation.

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• #9easysometimes asked

  9. Binary Tree Inorder Traversal

  Return the inorder (left, root, right) traversal of a binary tree's nodes. PayPal asks this to test stack-based iterative thinking — the same scaffolding used to walk a transaction-tree where parent transactions point at children (settlement → captures → auths).

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• #10easysometimes asked

  10. Same Tree

  Given two binary trees, decide if they are structurally identical and the nodes have the same values. PayPal asks this as a recursion warm-up — the same shape used when diffing two snapshots of a transaction-state tree to detect tampering or replay.

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• #11easysometimes asked

  11. Symmetric Tree

  Decide whether a binary tree is a mirror of itself. PayPal uses this as a recursion check — testing whether you can write a helper that compares two trees with mirrored axes, the same pattern they use for symmetric-link reconciliation between buyer-side and seller-side transaction graphs.

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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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• #13easysometimes asked

  13. Path Sum

  Determine whether a binary tree has a root-to-leaf path whose node values sum to a given target. PayPal uses this to test recursive tree traversal and base-case handling under financial-rule evaluation scenarios.

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• #14easysometimes asked

  14. Pascal's Triangle

  Generate the first numRows rows of Pascal's triangle where each element is the sum of the two elements above it. PayPal asks this to evaluate 2D array construction skills and pattern recognition relevant to combinatorial financial modeling.

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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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• #16easysometimes asked

  16. Single Number

  Find the one element in an array that appears exactly once while all others appear exactly twice. PayPal uses this to probe XOR bit-manipulation knowledge and constant-space thinking — skills tied to low-level transaction-ID deduplication logic.

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