DSA topics, without the fluff

Contiguous, index-addressable sequences. The substrate under half of all coding interviews — two-pointers, sliding-window, prefix-sums, and binary search all live here.

If you can't move two pointers confidently, you can't solve the other 80%.

Practice questions

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O(1) lookup in exchange for space. The "trade memory for time" lever — frequency counts, two-sum patterns, grouping, de-duplication.

Spotting the hash-map shape is usually the gap between a brute-force and an accepted solution.

LIFO and FIFO. Monotonic stacks for next-greater-element problems, queues for BFS, deques when you need both ends.

When the problem says "next larger" or "matching brackets," a stack is usually the answer.

Pointer-based sequences. Reversal, cycle detection, fast/slow pointers, and merge patterns. A classic whiteboard warm-up.

Interviewers love them because bugs here reveal who actually understands pointers.

Hierarchical structures — binary trees, BSTs, tries, heaps. Traversals (inorder, preorder, postorder, level-order), recursion, and lowest-common-ancestor patterns.

Tree recursion is the cleanest test of whether you can reason about a function calling itself.

Nodes and edges, directed or undirected. BFS, DFS, cycle detection, topological sort, union-find. Everything connectivity-shaped.

Once you can model a problem as a graph, the algorithms come off the shelf.

Decompose into overlapping subproblems with optimal substructure. Memoization and tabulation; 1D and 2D state.

The topic most candidates fake understanding of. Interviewers know. Get real reps in.

Big-O as a working tool, not a recitation. O(1), O(log n), O(n), O(n log n), O(n²) — and when each shows up in practice.

Every interviewer asks "what's the time complexity?" after the code works. Have a real answer.

Practice questions

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