Stop grinding random problems. Learn the reusable patterns behind them — each with a template, a worked example, and instant practice on our built-in code judge.
Start Pattern 0 →In order — each pattern builds on the previous. Finish with the one-page cheat sheet.
The meta-skill of coding interviews: reading a problem statement and mapping it to the right algorithmic pattern — with a signal-to-pattern cheat table.
The two-pointers technique: converging pointers on sorted arrays, reader/writer pointers for in-place edits, with templates and judge problems.
The sliding window pattern for substring and subarray problems: fixed and variable windows, the grow/shrink template, and judge practice.
The two hashmap patterns that solve half of all easy-medium interview problems: existence lookup and frequency counting, with templates.
Floyd's tortoise-and-hare technique: detect linked list cycles, find the middle node, and why two speeds guarantee a meeting.
The intervals pattern: sort by start then sweep, merging overlaps — with the overlap test and the classic meeting-rooms variants.
Binary search beyond lookups: first/last occurrence, rotated arrays, and binary-searching the answer space — with the universal template.
The three stack patterns in interviews: bracket matching, processing with undo, and the monotonic stack for next-greater-element problems.
The breadth-first search pattern: level-order traversal with a queue, why BFS finds shortest paths, and the grid-BFS template.
Depth-first search and backtracking: flood fill, connected components, and the choose-explore-unchoose template for permutations and combinations.
The Top-K pattern: when to sort vs heap, the size-K heap trick, frequency + heap combos, and a JS min-heap you can write in interviews.
Prefix sums for instant range queries and Kadane's algorithm for maximum subarray — the two tools for subarray-sum problems.
Master the in-place reversal pattern: reverse a full list, a sublist, and in K-groups — with the prev/cur/next choreography.
A practical DP framework: recognise it, define the state, write the recurrence — with climbing stairs, house robber and coin change solved.
The greedy pattern: making the locally optimal choice, when it works vs fails, and the classic interval-scheduling and jump-game examples.
Matrix interview patterns: spiral traversal, 90° rotation via transpose+reverse, and in-place marking tricks — with templates.
One-page revision sheet: every coding interview pattern with its trigger signal, complexity, template one-liner and judge problem.
One pattern unlocks dozens of problems. 15 lessons beat 500 random grinds.
Every lesson gives a code template to adapt — the exact shape to write under pressure.
Solve real problems with hidden tests on our DSA judge — right after each lesson.
Each lesson includes the exact sentences that score points with interviewers.