Master Data Structures & Algorithms with Kernel Queen
Categorized problems, clear video walkthroughs, and written guides. Track everything you solve, right in your browser, no account needed.
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Open roadmap →322 problems waiting. Your progress saves automatically in this browser.
Learn by category
322 hand-picked problems across 15 topics.
Arrays & Hashing
Hash maps, frequency counting, prefix sums, and matrix manipulation, the foundation.
Strings
Parsing, building, and transforming strings and substrings.
Two Pointers
Walk a sequence from both ends or at different speeds for O(n) solutions.
Sliding Window
Maintain a moving range to answer subarray/substring questions efficiently.
Stack & Queue
LIFO/FIFO thinking: matching, monotonic stacks, and ordered processing.
Binary Search
Halve the search space each step, on arrays and on answers.
Linked List
Pointer manipulation, fast/slow pointers, and in-place reversal.
Trees & Tries
DFS, BFS, and recursion over binary trees, BSTs, and tries.
Heap / Priority Queue
Always grab the smallest or largest next, top-K and scheduling problems.
Backtracking
Explore all candidates by building and undoing choices.
Graphs
Traversal, shortest paths, union-find, and topological order.
Dynamic Programming
Break problems into overlapping subproblems, the interview boss level.
Greedy
Make the locally optimal choice and prove it stays optimal.
Math & Geometry
Number theory, combinatorics, and geometric reasoning.
Bit Manipulation
Solve with XOR, masks, and bit tricks.
From the blog
All articles →Two Sum, From Brute Force to O(n)
The classic warm-up. Learn how a hash map turns an O(n²) scan into a single O(n) pass.
Arrays & HashingContains Duplicate, Your First Hash Set
A one-liner that teaches the single most useful data structure for interviews: the hash set.
StackValid Parentheses, The Stack's Greatest Hit
Matching brackets is the canonical stack problem. Learn the push/pop pattern you'll reuse everywhere.
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