70 DSA interview questions organized by pattern

Recognize the shape

Patterns reduce the search space

An unfamiliar problem becomes easier when you identify its structure. Sorted input suggests binary search or two pointers. A contiguous range suggests a sliding window or prefix sums. Dependencies suggest a graph.

Pattern recognition does not replace reasoning. It gives you a smaller set of ideas to test against the constraints.

Two pointers and sliding windows
Hash maps and prefix sums
Stacks, queues, and heaps
Trees, graphs, backtracking, and dynamic programming

DSA interview questions grouped by problem-solving pattern — The concept at a glance. The sections below turn each part into a practical decision.

A repeatable interview flow

Explain before you optimize

Restate the input, output, constraints, and edge cases. Describe a correct baseline, measure its cost, and then improve the expensive part.

Talk through the invariant while coding. A clear invariant makes the solution easier to verify than a line-by-line narration.

Use the constraintsAn input size near 10⁵ usually rules out O(n²) work and directs you toward linear or O(n log n) solutions.

Build durable recall

Use spaced revision instead of one long sprint

Re-solve missed questions after one day, one week, and one month. Change the values or constraints so you must reconstruct the idea.

Track the pattern and failure reason, not only whether the final code passed.

YAML

problem: longest-substring-without-repeat
pattern: sliding-window
failed_on: duplicate-removal
review: [tomorrow, next-week, next-month]

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