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The 21 DSA Topics That Cover 90% of Coding Interviews

The DSA topics that actually show up in interviews, ranked by how often they appear, so you know exactly what to master first and what to leave for last.

Riya Kushwaha, DSA Tracker team3 min readUpdated
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Coding interviews feel infinite, but they're not. A surprisingly small set of patterns covers the overwhelming majority of what gets asked. If you order your study by frequency rather than by textbook chapter, you become interview-ready far sooner, because you're solid on the high-probability material before you've touched the rare stuff.

Here are the 21 topics, grouped by how often they actually appear.

Tier 1: shows up constantly (master these first)

  1. Arrays & strings: the substrate of everything.

  2. Hashing / hash maps: the single most valuable tool.

  3. Two pointers

  4. Sliding window

  5. Binary search, and its sneaky "search on answer" variant.

  6. Sorting, plus knowing when not to sort.

  7. Recursion & backtracking

Tier 2: shows up often (master before any real interview)

  1. Linked lists

  2. Stacks & queues (incl. Monotonic stack)

  3. Trees: traversals, BST properties.

  4. Heaps / priority queues: top-K is everywhere.

  5. Graphs: BFS, DFS, topological sort.

  6. Dynamic programming: the 1D and 2D classics.

  7. Greedy

  8. Intervals

Tier 3: shows up sometimes (role- and level-dependent)

  1. Bit manipulation

  2. Tries

  3. Union-Find (DSU)

  4. Shortest paths (Dijkstra, Bellman-Ford)

  5. Advanced DP (DP on trees, bitmask DP)

  6. Segment trees / Fenwick trees: rare outside competitive-leaning loops.

How to spend your time

Spend roughly half your prep on Tier 1, a third on Tier 2, and only what's left on Tier 3. The common failure is inverting this: burning weeks on segment trees while shaky on hashing. Interviewers sample from the top of this list far more than the bottom.

Your target role shifts a few items up or down (backend pulls graphs up; frontend pulls them down), but Tier 1 is universal. Anchor there, then specialise. If you want this sequencing handled for you across the Apna College, Love Babbar, and Striver sheets at once, that's what DSA Tracker does.

How big each topic actually is

Frequency is one measure; the size of each topic in a curated sheet is another, and the two do not always agree. In DSA Tracker's 370-problem set the largest topics are Dynamic Programming with 51 problems, Graph with 48, Arrays with 34, Binary Trees with 32 and Strings with 22. The smallest are Queue with 4, Intervals with 5, Two Pointers and Matrix with 6 each. Dynamic programming is large because it has many distinct shapes to learn, not because every interview asks it; two pointers is small because one idea covers the whole topic. So the rule holds: master the small, universal Tier 1 topics first, since a handful of problems each makes you fluent, and budget real weeks for trees, graphs and dynamic programming, which are large because they are genuinely broad. A first problem for each, in that order: Two Sum, 3Sum, Binary Search, Reverse Linked List, Binary Tree Level Order Traversal, Number of Islands, Climbing Stairs.

Further reading: Binary search on Wikipedia.

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Frequently asked questions

Which DSA topic is asked the most in interviews?

Arrays with hashing. Almost every first-round problem is an array or string question that a hash map turns from quadratic into linear. Two pointers, sliding window and binary search follow, then trees and graphs in later rounds.

Which DSA topics can I leave for last?

Bit manipulation, tries, union-find, advanced dynamic programming and segment trees. They appear in specific roles and competitive-leaning loops, so learn them after the high-frequency tiers are solid, or when a target company is known to ask them.

How should I split my time across topics?

Roughly half on the first tier, a third on the second, and the remainder on the third. Inverting that split, weeks on segment trees while shaky on hashing, is the most common way to be unprepared with a lot of hours logged.

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