Representative Hash Table problems
Find the length of the longest substring without repeating characters using a sliding window and hash map to track state efficiently.
Open problem page#12 Integer to RomanConvert a given integer to its Roman numeral representation using hash table mapping and decimal place math operations efficiently.
Open problem page#13 Roman to IntegerConvert a Roman numeral string into an integer using a hash table and mathematical principles to determine value order.
Open problem page#17 Letter Combinations of a Phone NumberGenerate all letter combinations a digit string can represent using backtracking with pruning, leveraging hash table mapping efficiently.
Open problem page#30 Substring with Concatenation of All WordsFind all starting indices of substrings in a string that are concatenations of a given list of words.
Open problem page#36 Valid SudokuCheck if a 9x9 Sudoku board is valid by scanning rows, columns, and sub-boxes with hash lookups, ensuring no duplicates exist.
Open problem page#37 Sudoku SolverSolve the Sudoku puzzle by filling empty cells while respecting Sudoku's rules using array scanning and backtracking.
Open problem page#41 First Missing PositiveIdentify the smallest missing positive integer in an unsorted array using constant space and linear time scanning techniques.
Open problem page#49 Group AnagramsGroup the anagrams in a list of strings using efficient hash table-based methods, focusing on array scanning.
Open problem pageHash Table interview questions usually collapse into a small set of repeatable moves. This page groups those GhostInterview problem pages together so you can stay inside one pattern family, compare representative questions, and practice explanations that transfer across multiple prompts. If you are trying to sharpen one interview weakness instead of browsing the entire library, start here.
Why Hash Table Matters In Coding Interviews
Interviewers rarely care about the label alone. They care about whether you can recognize when the Hash Table pattern applies, explain why it applies, and avoid the failure modes that usually show up under time pressure. That is why this page focuses on the family of problems rather than a single isolated example.
Pattern families that show up here
- Array scanning plus hash lookup
- Hash Table plus String
- Sliding window with running state updates
Use this page to narrow the session
Start from this topic hub, choose one or two representative problems, and then open the detailed problem pages only after you know which version of the pattern you want to reinforce.
How To Practice This Topic
The best workflow is to keep the prep block narrow. Pick one easy or medium problem to confirm the base pattern, then one medium or hard problem to test whether the explanation still holds when the constraints tighten. Once the logic is stable, move into GhostInterview to rehearse the live explanation flow.
Focus on transfer, not title count
Solving more Hash Table titles is less useful than understanding how the same move changes across examples. Try to describe what stays the same and what changes from one problem to the next.
Use the problem page when you want the exact breakdown
This topic hub is the discovery layer. The single-problem pages are where you get the answer-first summary, examples, constraints, approach, complexity, pitfalls, and solver CTA.
How GhostInterview Fits
GhostInterview works best after you know which pattern family you are inside. Use this page to choose the right Hash Table problem, then use the solver to get the answer path, complexity framing, and follow-up support without switching into a generic study flow.
FAQ
What does the Hash Table topic usually test in interviews?
Hash Table questions usually test whether you can spot the underlying pattern quickly, explain the trade-offs, and move from intuition to implementation without losing clarity.
How should I use this Hash Table topic page?
Use it as a pattern hub. Start with the representative problems on this page, compare the common approach, and then open the exact problem page when you want the full breakdown.
How many GhostInterview problem pages are in the Hash Table group?
This topic page currently groups 610 indexed GhostInterview problem pages under the Hash Table family.
Should I practice this topic before harder patterns?
That depends on your current gaps. If Hash Table is already a weak spot in interviews, it is usually better to stabilize it first before moving into more advanced or less frequent patterns.
Where does GhostInterview fit once I pick a Hash Table problem?
The topic page narrows the pattern family. The problem page gives the exact breakdown. GhostInterview is the solver layer when you need direct help with execution, complexity, and follow-up handling.
Stay close to the same reasoning family
Need direct help once you choose a Hash Table problem?
Use GhostInterview as the solver layer after you select the exact prompt. Capture the question, get the answer path and complexity framing, and keep the workflow inside the same topic family.