Representative Counting problems
Find the majority element in an array, where the element appears more than n/2 times, using efficient algorithms.
Open problem page#229 Majority Element IIIdentify all elements in an integer array appearing more than ⌊ n/3 ⌋ times using efficient array scanning and hash counting techniques.
Open problem page#299 Bulls and CowsSolve the Bulls and Cows problem using hash tables and string manipulation to track exact and misplaced digits.
Open problem page#347 Top K Frequent ElementsFind the k most frequent elements from an array using efficient algorithms like hashing and sorting.
Open problem page#383 Ransom NoteDetermine if a ransom note can be constructed from a magazine's letters using hash tables and string counting techniques.
Open problem page#387 First Unique Character in a StringFind the index of the first non-repeating character in a string using efficient queue-driven state processing.
Open problem page#451 Sort Characters By FrequencySort Characters By Frequency requires counting characters efficiently and rearranging a string in descending frequency order for clarity.
Open problem page#594 Longest Harmonious SubsequenceFind the length of the longest harmonious subsequence in an integer array using array scanning and hash-based frequency counting techniques.
Open problem page#621 Task SchedulerTask Scheduler is solved by counting task frequencies and computing how cooldown gaps force idle slots around the most frequent task.
Open problem pageCounting 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 Counting Matters In Coding Interviews
Interviewers rarely care about the label alone. They care about whether you can recognize when the Counting 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
- Greedy choice plus invariant validation
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 Counting 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 Counting 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 Counting topic usually test in interviews?
Counting 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 Counting 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 Counting group?
This topic page currently groups 149 indexed GhostInterview problem pages under the Counting family.
Should I practice this topic before harder patterns?
That depends on your current gaps. If Counting 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 Counting 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 Counting 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.