Computing running medians on a stream of numbers pops up in real-time analytics, financial tickers, and sensor dashboards. You need to support two operations—adding a number and retrieving the current median—both in sublinear time.

Caching is critical in systems design, from web browsers to database engines. An LRU (Least Recently Used) cache evicts the least recently used entry when full, ensuring hot data stays accessible. Implementing one in code tests your mastery of linked lists, hash maps, and constant-time operations.

Combining multiple sorted streams into one sorted output is a classic challenge faced in database merge operations, log file aggregation, and external sorting. The “merge K sorted lists” problem tests your ability to coordinate multiple pointers, leverage priority data structures, and keep everything running in optimal time.

Checking for nearby repeated events in a log or sensor stream is a common task in monitoring, fraud detection, and real‑time analytics....

Finding the longest run of consecutive days, IDs, or timestamps in a dataset comes up in analytics, event processing, and scheduling systems. This “Longest Consecutive Sequence” problem is a great way to exercise hashing, set membership, and thinking about how to avoid redundant work.

Finding how many contiguous stretches of transactions sum to a target turns up in budgeting tools, analytics dashboards, and real‑time...

Clustering words that are anagrams of each other is a classic interview problem and mirrors real‑world tasks like building search indexes...

Circular queues (ring buffers) come up in real‑world systems like streaming data buffers, IO scheduling, and task schedulers. They let...

Reverse Polish Notation (RPN), also known as postfix notation, is a useful format for calculators and expression evaluation because it...

Maintaining a stack that can return its minimum value in constant time is a neat warm‑up that mirrors real‑world needs like tracking the...

Building a queue out of stacks is a classic exercise in adapting one data structure to mimic another. It’s not only a great warm‑up for...

Checking whether a string of parentheses is valid is one of the most common warm‑ups in interviews. It’s directly applicable to parsing...

Flattening a multilevel doubly linked list pops up in real‑world scenarios like expanding nested comment threads or unfolding embedded...

Finding the intersection node of two linked lists is like spotting the shared checkpoint in two runners’ paths—useful for debugging...

Adding two numbers digit by digit in reverse order is a great warm‑up for handling arbitrary‑precision arithmetic in systems that store...

Checking whether a linked list reads the same forwards and backwards is a great warm‑up that mirrors real‑world tasks like validating...

Removing the Nth node from the end of a linked list is a perfect warm-up for real-world tasks like trimming logs, pruning history...

Finding not just whether a linked list has a cycle but exactly where that cycle begins is a real-world need whenever you’re dealing with...

Detecting a cycle in a linked list is a classic problem that comes up when you need to guard against infinite loops—whether you’re...

Merging two sorted linked lists is like merging two sorted streams of data—think combining two user event logs in chronological order....