Coinbase Coding Interview Questions
28 Coinbase coding interview problems with full optimal solutions — 16 easy, 9 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 Coinbase interviewer values, and a FAQ section.
- #17mediumfoundational
17. Top K Frequent Elements
Surface the K most-traded assets on an exchange — Coinbase uses this problem to test whether you reach for a heap over a naive sort when ranking trade volumes across thousands of instruments.
- #18mediumfoundational
18. Coin Change
Compute the fewest denominations to reach an exact value — Coinbase uses this DP classic to see how you model currency conversion and minimum-fee routing across crypto denominations.
- #19mediumfoundational
19. Merge Intervals
Collapse overlapping trading windows into consolidated ranges — Coinbase uses interval merging to evaluate how engineers reason about time-series events like order-book snapshots and candlestick aggregation.
- #20mediumfoundational
20. Min Stack
Track the minimum portfolio value at O(1) cost — Coinbase asks this to test whether you can maintain auxiliary state for instant low-watermark reads without rescanning the full price history.
- #21mediumfoundational
21. LRU Cache
Build a fixed-capacity account-data cache that evicts the least-recently-used entry — Coinbase uses this design question to measure whether you can combine a hash map and a doubly-linked list for O(1) reads and writes.
- #22mediumfoundational
22. Number of Islands
Count disconnected clusters in a grid — Coinbase maps this to partitioning liquidity pools or detecting isolated market segments that cannot route to a shared settlement layer.
- #23hardfoundational
23. Sliding Window Maximum
Extract the peak price across every k-candle trading window in O(n) — Coinbase uses this problem to stress-test whether you can maintain a monotonic deque instead of repeatedly scanning a window when computing rolling highs on order-book snapshots.
- #24hardfoundational
24. Trapping Rain Water
Calculate total liquidity trapped between price-bar barriers — Coinbase uses this classic to evaluate whether engineers can reason about prefix/suffix maximums and then collapse the solution to a two-pointer scan without extra arrays.
- #25mediumfoundational
25. Longest Substring Without Repeating Characters
Find the longest run of unique trading-pair symbols in a sequence — Coinbase uses sliding-window problems to evaluate how you model streaming data with a shrinking-left-boundary technique common in real-time feed deduplication.
- #26mediumfoundational
26. K Closest Points to Origin
Retrieve the K accounts with the smallest distance from a reference price level — Coinbase uses this heap problem to test real-time top-K selection, the engine behind their order-proximity ranking in the matching engine.
- #27mediumfoundational
27. Network Delay Time
Find the worst-case latency before a broadcast reaches every node — Coinbase uses Dijkstra problems to evaluate how engineers reason about minimum-cost routing across crypto-network relay nodes and cross-chain bridging hops.
- #28hardfoundational
28. Find Median from Data Stream
Maintain the real-time median bid price as orders stream in — Coinbase uses this dual-heap problem to test whether engineers can design O(log n) insert / O(1) median structures for continuous market-data feeds.
- #1easyfrequently asked
1. Two Sum
Given an array of integers and a target, return the indices of two numbers that add up to the target. Coinbase asks this as a warm-up to gauge whether you reach for hash maps over nested loops on the very first problem.
- #2easyfrequently asked
2. Valid Parentheses
Determine if a string of brackets is balanced and properly nested. Coinbase uses this to test stack fundamentals — order-book matching engines lean on the same LIFO discipline.
- #3easyfrequently asked
3. Merge Two Sorted Lists
Splice two sorted linked lists into one sorted list. Coinbase uses this to test pointer manipulation — a common building block when merging streams of order-book updates from different feeds.
- #4easysometimes asked
4. Remove Duplicates from Sorted Array
Compact a sorted array in place so each element appears once and return the new length. Coinbase uses this to probe pointer-discipline — the same two-pointer trick deduplicates trade prints with the same sequence number.
- #5easysometimes asked
5. Remove Element
Remove all occurrences of a target value from an array in place. Coinbase uses this as a quick filter to confirm you reach for two-pointer compaction before allocating.
- #6easyfrequently asked
6. Search Insert Position
Given a sorted array, find the index where a target should be inserted to maintain order. Coinbase asks this because it's the building block for inserting a new limit order at the right price level in an order book.
- #7easyfrequently asked
7. Maximum Subarray
Find the contiguous subarray with the largest sum. Coinbase asks this to test the local-vs-global pattern — the same shape shows up when finding the most profitable contiguous holding window in price data.
- #8easysometimes asked
8. Plus One
Increment a big integer represented as a digit array by one. Coinbase uses this as a warm-up before the inevitable BigInt and precision-handling follow-ups.
- #9easyfrequently asked
9. Merge Sorted Array
Merge two sorted arrays in place, with nums1 sized large enough to hold both. Coinbase asks this because in-place merges show up everywhere in matching engines — the destination buffer is already allocated.
- #10easysometimes asked
10. Binary Tree Inorder Traversal
Return the inorder traversal of a binary tree's values. Coinbase asks this to confirm you can do both recursive and iterative tree walks — iterative is the one you'd use to walk a price-level tree without blowing the stack.
- #11easysometimes asked
11. Same Tree
Determine whether two binary trees are structurally identical with equal values. Coinbase asks this as a warm-up for tree-equivalence and snapshot-comparison follow-ups.
- #12easyrarely asked
12. Symmetric Tree
Check whether a binary tree is a mirror of itself. Coinbase uses this to confirm you can recurse on pairs — the same pattern used to compare a bid ladder with its ask mirror.
- #13easysometimes asked
13. Maximum Depth of Binary Tree
Return the depth of a binary tree. Coinbase uses this to verify recursion fundamentals before moving to harder tree problems.
- #14easysometimes asked
14. Balanced Binary Tree
Determine if a binary tree is height-balanced. Coinbase uses this to test the post-order short-circuit pattern — the same trick used to validate constraints across an order-book tree.
- #15easyrarely asked
15. Minimum Depth of Binary Tree
Return the minimum depth — the number of nodes along the shortest path from root to nearest leaf. Coinbase asks this to test whether you spot the asymmetric edge case where one child is null.
- #16easyrarely asked
16. Pascal's Triangle
Generate the first numRows of Pascal's triangle. Coinbase asks this to test array-building discipline and to set up follow-ups on combinatorics (used in risk-pricing).
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