// problem set
Every problem is framed against work a scientist already does, with layered hints for when you're stuck. Filter by difficulty or track and pick your first one.
// 12 problems shown
Two-Pointer Sum
Find the two readings whose values add up to a target. Your first real interview pattern.
Valid Bracket Sequence
Validate nested brackets with a stack — the canonical “do you know when to use a stack” question.
Rolling Window Mean
Compute the maximum average over any fixed window — a pattern you already use to smooth noisy data.
Merge Overlapping Intervals
Collapse overlapping ranges into clusters — think peak-calling, but as an interview staple.
Search the Sorted Threshold
Find a value in a sorted array in O(log n). The algorithm behind every fast lookup.
Lab Network Reachability
Decide whether one node can reach another in a directed graph — your first traversal.
Counting Distinct Paths
Your gateway to dynamic programming — count the ways to reach the top.
Group by Signature
Bucket strings by a canonical key — the same move as grouping samples by signature.
Design an LRU Cache
A full system-design-in-miniature: O(1) get and put with eviction. The classic Hard.
Median of a Data Stream
Maintain a running median over a stream — the two-heap pattern senior interviews love.
Top K Frequent Elements
Surface the most common values fast — exactly what you do when you rank counts in a dataset.
Shortest Transformation
Find the shortest mutation path between two words — BFS on an implicit graph.