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DSA interview patterns

A small number of patterns cover most coding interview questions. The skill that actually matters is recognizing which pattern applies to an unfamiliar prompt — not having memorized a solution to a similar-looking problem.

Why patterns beat memorization

LeetCode has over 3,000 problems. Nobody memorizes 3,000 solutions, and interviewers know it — which is exactly why almost no interview question is genuinely novel. It is a known pattern wearing an unfamiliar story: "find the longest substring without repeating characters" and "find the smallest window containing all target characters" are the same sliding-window skeleton with different exit conditions. The candidates who do well are not the ones who have seen the most problems — they are the ones who can look at a new prompt and correctly answer "what does this resemble."

Each topic below leads with recognition cues — the specific words and structures in a problem statement that point to that pattern — before getting into how the pattern actually works.

The 8 patterns

Arrays & Hashing

Recognize it: "Have I seen this value before" or "count occurrences of something"

Two Pointers

Recognize it: A sorted array or string, looking for a pair or a palindrome property

Sliding Window

Recognize it: A contiguous subarray or substring with a size or sum constraint

Binary Search

Recognize it: A sorted (or monotonic) search space, or "find the boundary where a condition flips"

Stacks & Queues

Recognize it: Matching pairs, nesting, or "process in the order things arrived / most-recent-first"

Trees & Traversals

Recognize it: A hierarchical structure — anything with "node," "parent," or "ancestor" in the prompt

Graphs & BFS/DFS

Recognize it: "Connections" between things, shortest path, or "can you get from A to B"

Dynamic Programming

Recognize it: A brute-force recursive solution that recomputes the same subproblem repeatedly

Two concepts that decide whether interviewers trust your answer

A correct solution delivered silently, with no complexity statement, scores worse than the same solution narrated clearly with its trade-offs stated out loud. These two pages cover the skills that sit underneath every pattern above.

Time & Space Complexity

Stating and defending the Big-O of your own solution under questioning

Thinking Out Loud

What to actually say while you code, and why silence costs you points

Frequently asked questions

Do I need to memorize all 8 patterns before interviewing?
You need to recognize them, not recite their names. Most candidates who "know" a pattern from a course still freeze when the same pattern appears in an unfamiliar prompt — the recognition cues on each topic page exist specifically to close that gap.
Which pattern should I learn first?
Arrays & Hashing and Two Pointers. Together they cover the largest share of early-loop questions and most other patterns build on the intuition of "what am I storing, and what am I looking up."
Are these patterns the same at every level?
The patterns are identical from SDE 1 through Staff. What changes by level is emphasis and difficulty ceiling — DSA is most of an SDE 1 interview and a brief sanity check by Staff. See interview prep by level for the specifics at your target level.

Related

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