Maintain a contiguous range and slide its boundaries to avoid recomputation.
Time O(n), space O(1) or O(k) for a frequency map.- Pharmacy Pickup
- Rolling Peak Sensor
- Unique DNA Run
A 12-pattern alternative to the Blind 75.
Replace a 75-problem list with 12 patterns. Each pattern covers dozens of problems once the shape clicks. The same fluency, a better mental organizer.
Two cursors moving independently over a sorted or monotone structure.
Time O(n) after an optional O(n log n) sort; space O(1).- Scale Balancer
- License Plate Mirror
- Triple Alloy
A stack whose elements stay in non-increasing or non-decreasing order.
Time O(n) amortized (each element is pushed and popped once).- Next Rainy Day
- Skyline Vault
- Convoy Merge
Precompute cumulative arrays so range queries answer in O(1).
Preprocess O(n); query O(1).- Exclusive Revenue
- Range Tally
- Running Balance
When a predicate is monotonic over the answer space, binary search the answer itself.
Time O(log R · feasibility(n)) where R is the answer range.- Bandwidth Throttle
- Hiker's Ridge
- Deadline Bake
A data structure that returns the min or max in O(log n) per operation.
Insert/pop O(log n); peek O(1); heapify O(n).- Leaderboard Live-Rank
- Barista Rotation
- Multi-Feed Merger
A disjoint-set data structure supporting near-constant merge and find.
Amortized O(α(n)) per op with path compression + union by rank.- Friend-Circle Counter
- Extra Cable Finder
- LAN Mesh Audit
Linear ordering of a DAG consistent with its dependencies.
Time O(V + E); space O(V).- Build-Order Planner
- Dialect Sorter
- Certification Track
Breadth-first for shortest unweighted paths; depth-first for exhaustive traversal.
Time O(V + E); space O(V).- Oil Patch Count
- Firefront Spread
- Exit-Sign Distances
Break an overlapping-subproblem problem into a recurrence and cache results.
State × transition cost; typical O(n), O(n²), or O(n·m).- Ski Lift Tolls
- DNA Commonality
- Typo Repair Cost
#11
Backtracking
DFS through a decision tree with pruning and state restoration.
Exponential in the decision depth; pruning is the whole game.- Pizza Topping Combos
- Radar Placement
- Maze Inscription
Sort events by time, sweep a line, maintain an active set for overlap questions.
Time O(n log n) for the sort; O(n) for the sweep.- Meeting Room Budget
- Event Merge
- Skyline Silhouette
Frequently asked questions
- What's the best alternative to the Blind 75?
- A 12-pattern study plan: sliding window, two pointers, monotonic stack, prefix and suffix, binary search on answer, heap, union-find, topological sort, graph BFS/DFS, dynamic programming, backtracking, and interval sweep. Each pattern generalizes to dozens of problems.
- How is this different from the Blind 75?
- The Blind 75 is a list of 75 specific problems. The 12-pattern alternative is a curriculum indexed by concept. You stop memorizing problems and start recognizing shapes.
- How long does the 12-pattern alternative take?
- Typical pace: one pattern per 3–4 days, with the first week producing fluent recognition of 3–4 patterns. Full fluency across all 12 takes 8–12 weeks of consistent practice.
- Do I still need to do LeetCode or NeetCode problems?
- For volume and time-pressure reps, yes — but use them to instantiate each pattern rather than as the organizing unit.
Run the free diagnostic.
Ten-minute patterns quiz. No card. Personalized loop starts on the other side.