HP Coding Interview Questions
25 HP 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 HP interviewer values, and a FAQ section.
Showing 16 problems of 25
- #3mediumfrequently asked
3. Longest Substring Without Repeating Characters
HP's document-processing and OCR pipelines apply sliding-window algorithms for character-sequence analysis in scanned text streams. This problem is a textbook sliding-window exercise — HP uses it to confirm that candidates can translate a brute-force nested loop into an O(n) single-pass scan.
- #15mediumfrequently asked
15. 3Sum
HP enterprise analytics pipelines perform multi-dimensional range queries and constraint-satisfaction checks on device telemetry. 3Sum is the canonical multi-pointer problem — HP uses it to evaluate whether you can methodically eliminate the cubic brute force down to quadratic through sorting and pointer discipline.
- #20easyfrequently asked
20. Valid Parentheses
Parsing structured expressions is core to HP's firmware configuration parsers and printer command languages (PCL/PJL). Valid Parentheses tests whether you can maintain state with a stack — the same discipline behind device-command validation.
- #21easyfrequently asked
21. Merge Two Sorted Lists
HP's device-driver and print-spooler stacks frequently merge ordered queues of pending jobs from multiple input sources. Merging two sorted linked lists is the fundamental building block — HP uses it to verify that candidates handle pointer manipulation without losing data.
- #49mediumfrequently asked
49. Group Anagrams
HP document and content management systems aggregate files with equivalent names or metadata under a unified key. Group Anagrams is a proxy for that canonical key-design question: how do you derive a consistent, collision-free key from unordered data? HP uses it to test hashing intuition.
- #53easyfrequently asked
53. Maximum Subarray
HP uses signal-processing algorithms in imaging and scanning products where finding the strongest contiguous signal window is a real computational task. Maximum Subarray (Kadane's algorithm) is the archetype: HP interviewers use it to test whether you can identify the single-pass greedy insight in a DP-flavored problem.
- #56mediumfrequently asked
56. Merge Intervals
HP enterprise IT scheduling tools manage maintenance windows, firmware update slots, and print-fleet reservation blocks. Overlapping intervals must be collapsed into non-overlapping ranges before scheduling can proceed. Merge Intervals is the canonical version of this problem, and HP uses it to test sort-then-sweep reasoning.
- #70easyfrequently asked
70. Climbing Stairs
Dynamic programming is central to HP's ink/toner optimization algorithms and cost-scheduling tools for enterprise print fleets. Climbing Stairs is the textbook DP entry point — HP uses it to confirm that candidates understand memoization and state transition before discussing more complex optimization problems.
- #121easyfrequently asked
121. Best Time to Buy and Sell Stock
HP's financial and enterprise analytics teams process time-series data from equipment telemetry and cost-optimization pipelines. This problem tests single-pass reasoning over sequential data — the same pattern used when scanning sensor readings for peak-to-trough performance differences.
- #146mediumfrequently asked
146. LRU Cache
HP's firmware and print-spooler stacks manage limited on-device memory with LRU eviction policies for rendered page segments and font caches. LRU Cache is not just a puzzle — it mirrors a real design decision in HP hardware. Interviewers use it to test whether you can compose two data structures to satisfy a compound O(1) requirement.
- #200mediumfrequently asked
200. Number of Islands
HP's imaging and scanning systems detect contiguous regions of ink, toner, or light to distinguish characters and objects on a page. Number of Islands is the archetypal connected-components problem that underlies this region-detection logic — HP uses it to test BFS/DFS grid traversal for systems roles.
- #206easyfrequently asked
206. Reverse Linked List
HP's systems software and firmware teams deal with linked structures constantly — job queues, device-descriptor chains, and print-spooler task lists. Reversing a linked list in-place is a fundamental pointer-manipulation exercise that HP uses to probe candidate comfort with low-level memory operations.
- #207mediumfrequently asked
207. Course Schedule
HP's firmware release pipeline enforces strict build-dependency ordering — drivers must compile before OS modules that depend on them, and cyclic dependencies block production releases. Course Schedule is the canonical cycle-detection-in-a-directed-graph problem that mirrors this real constraint. HP uses it to evaluate topological-sort and DFS fluency.
- #238mediumfrequently asked
238. Product of Array Except Self
HP's numerical calibration and imaging-pipeline software computes normalization factors that exclude each sensor's own reading. Product of Array Except Self — without using division — is a direct test of prefix/suffix product reasoning that appears naturally in HP's signal-processing and correction workflows.
- #322mediumfrequently asked
322. Coin Change
HP enterprise subscription and billing systems compute optimal denomination splits when processing payments or credits. Coin Change is the canonical unbounded-knapsack DP problem that HP uses to evaluate whether candidates can set up a state table, define a clean recurrence, and reason about the base case.
- #347mediumfrequently asked
347. Top K Frequent Elements
HP support and diagnostics tools rank error codes and telemetry events by frequency to surface the most impactful hardware failures. Top K Frequent Elements tests whether you can combine frequency counting with an efficient selection mechanism — a pattern used across HP's observability stack.