HubSpot Coding Interview Questions
25 HubSpot coding interview problems with full optimal solutions — 8 easy, 12 medium, 5 hard. Every problem ships with multiple approaches (brute-force first, then the optimal), complexity tables for each, company-specific tips on what an HubSpot interviewer values, and a FAQ section.
- #1easyfrequently asked
1. Two Sum
HubSpot uses Two Sum as a warm-up screen to see if you can jump straight from brute force to an O(n) hash-map solution while explaining your reasoning out loud — a habit their Boston engineering culture values deeply.
- #3mediumfrequently asked
3. Longest Substring Without Repeating Characters
HubSpot uses this sliding-window classic to test both the pattern itself and your ability to manage a moving window's state efficiently — directly applicable to deduplicating streaming event logs in their CRM activity feeds.
- #4hardoccasionally asked
4. Median of Two Sorted Arrays
HubSpot includes Median of Two Sorted Arrays to assess whether candidates can binary search on a partition index rather than on array values — a conceptual leap that separates strong algorithmic thinkers from those who rely on rote solutions.
- #9easyoccasionally asked
9. Palindrome Number
HubSpot asks Palindrome Number to see whether candidates look for math-based solutions before reaching for string conversion — a habit that signals strong algorithmic instincts beyond language-specific shortcuts.
- #15mediumfrequently asked
15. 3Sum
HubSpot asks 3Sum to test your ability to reduce a multi-pointer problem systematically — a key skill when de-duplicating and reconciling overlapping data records across their CRM's contact merge workflows.
- #20easyfrequently asked
20. Valid Parentheses
HubSpot asks Valid Parentheses to test stack intuition and edge-case discipline — skills that surface constantly when parsing template syntax, email tokens, or workflow expression strings in their CRM platform.
- #21easyfrequently asked
21. Merge Two Sorted Lists
HubSpot asks Merge Two Sorted Lists to evaluate pointer hygiene and recursive vs. iterative trade-offs — skills that translate directly to merging ordered event streams and sorted activity logs in their CRM timeline features.
- #23hardoccasionally asked
23. Merge K Sorted Lists
HubSpot asks Merge K Sorted Lists to see whether you can reason about multi-source merging with a priority queue — a design pattern central to their event-stream aggregation where k data sources need to be merged in order for the activity feed.
- #42hardoccasionally asked
42. Trapping Rain Water
HubSpot asks Trapping Rain Water to evaluate your ability to reason about bounded quantities — how much water a cell can hold is determined by the minimum of the tallest bars on its left and right — a constraint-propagation mindset they value in their data pipeline engineers.
- #49mediumfrequently asked
49. Group Anagrams
HubSpot frequently asks Group Anagrams because it tests canonical key generation for grouping — a fundamental skill in CRM data normalization where contacts or properties with different surface strings need to be clustered by canonical form.
- #53easyfrequently asked
53. Maximum Subarray
HubSpot asks Maximum Subarray to test Kadane's algorithm — one of the most elegant greedy/DP hybrids in the canon — and to see whether you can clearly articulate why dropping a negative prefix always improves the running sum.
- #56mediumfrequently asked
56. Merge Intervals
HubSpot asks Merge Intervals because overlapping-range problems appear constantly in their scheduling, deal-stage overlap detection, and meeting de-duplication workflows — and they want to see clean sort-then-scan logic with tight boundary handling.
- #70easyfrequently asked
70. Climbing Stairs
HubSpot uses Climbing Stairs as an entry point into dynamic programming thinking — they want to see you recognize overlapping subproblems and memoize rather than recompute, a discipline that directly applies to their complex workflow-evaluation engines.
- #98mediumfrequently asked
98. Validate Binary Search Tree
HubSpot asks Validate BST to test whether you understand the BST property beyond the naive 'left < root < right' check — they want to see you propagate valid range bounds through the recursion, a pattern that reflects the kind of constraint-passing thinking their backend engineers apply daily.
- #121easyfrequently asked
121. Best Time to Buy and Sell Stock
HubSpot includes this classic sliding-window / greedy problem to test whether you can track a running minimum while computing a maximum difference — a pattern that recurs in revenue-trend analysis across their sales CRM data pipelines.
- #127hardoccasionally asked
127. Word Ladder
HubSpot asks Word Ladder to test BFS on an implicit graph where nodes are words and edges are single-character transformations — a pattern that generalizes to shortest-path problems across their CRM entity relationship graph.
- #139mediumoccasionally asked
139. Word Break
HubSpot uses Word Break to test bottom-up dynamic programming and substring reachability — reasoning patterns that map directly to parsing HubSpot's expression language and evaluating segmented workflow conditions.
- #146mediumfrequently asked
146. LRU Cache
HubSpot asks LRU Cache because it's a real design problem embedded in a coding question — their platform caches CRM data aggressively, and engineers are expected to understand how eviction policies are implemented, not just configured.
- #200mediumfrequently asked
200. Number of Islands
HubSpot asks Number of Islands to test graph traversal fundamentals — BFS and DFS on an implicit grid — skills that transfer to connected-component analysis in their contact relationship graph and account hierarchy features.
- #206easyfrequently asked
206. Reverse Linked List
HubSpot includes Reverse Linked List to confirm you can manipulate pointer-based structures precisely — an essential skill for engineers working on their pipeline and activity-feed data models where ordered traversal matters.
- #207mediumoccasionally asked
207. Course Schedule
HubSpot asks Course Schedule to assess cycle detection in directed graphs — a pattern that arises in their workflow automation engine where circular dependency detection between triggers and actions is a critical correctness guarantee.
- #238mediumfrequently asked
238. Product of Array Except Self
HubSpot includes this problem to test prefix/suffix product reasoning without division — a constraint that forces you to think about the problem from two directions simultaneously, a hallmark of the kind of algorithmic clarity their Boston engineering team values.
- #297hardoccasionally asked
297. Serialize and Deserialize Binary Tree
HubSpot asks Serialize and Deserialize Binary Tree to test OOP design instincts alongside algorithmic thinking — you must design a codec that faithfully round-trips any tree structure, mirroring how their backend engineers design data serialization schemas for tree-structured CRM objects.
- #322mediumoccasionally asked
322. Coin Change
HubSpot uses Coin Change to probe unbounded knapsack / bottom-up DP thinking — the same pattern that underlies their pricing-plan composer and subscription credit allocation logic, where achieving an exact amount from discrete denominations matters.
- #347mediumfrequently asked
347. Top K Frequent Elements
HubSpot asks Top K Frequent Elements to test your knowledge of heap-based selection and bucket sort — patterns that power ranking and analytics features like 'top properties by usage' or 'most engaged contacts' across their marketing platform.
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