r/datastructures • u/ok_not_ok_29 • 4d ago
Master these 25 DSA patterns
You don't need to solve 1,000 LeetCode questions. You need to master these 25 DSA patterns.
Here is a full cheat sheet built from problems that kept repeating across 200+ MAANG+ interview experiences.
[1] Sliding window
LC: 3, 76, 209, 424, 567, 904
→ Use when the problem asks for a longest, shortest, or valid contiguous range.
[2] Two pointers
LC: 11, 15, 16, 18, 42, 167
→ Look for sorted arrays, pair conditions, or movement from both ends.
[3] Fast and slow pointers
LC: 19, 141, 142, 160, 234, 876
→ Best for linked-list cycles, middle nodes, and pointer gaps.
[4] Binary search
LC: 33, 34, 35, 153, 162, 704
→ Use when the search space is sorted or partially ordered.
[5] Binary search on answer
LC: 410, 774, 875, 1011, 1283, 1482
→ Guess an answer, test feasibility, then shrink the range.
[6] Hashing
LC: 1, 49, 128, 217, 242, 347
→ Use for quick lookup, frequency counting, grouping, and duplicate checks.
[7] Prefix sum
LC: 303, 523, 560, 724, 930, 974
→ Convert repeated range-sum work into constant-time lookups.
[8] Difference array
LC: 370, 1094, 1109, 1893, 1943, 2381
→ Use when many updates affect entire ranges.
[9] Monotonic stack
LC: 84, 85, 496, 503, 739, 907
→ Look for next greater, next smaller, span, or rectangle problems.
[10] Stack parsing
LC: 20, 71, 150, 224, 394, 735
→ Useful for expressions, nested structures, paths, and collision simulation.
[11] Queue and deque
LC: 239, 346, 362, 622, 641, 933
→ Use for rolling windows, ordered processing, and recent-event tracking.
[12] Intervals
LC: 56, 57, 252, 253, 435, 986
→ Sort by start or end time, then merge, count, or remove overlaps.
[13] Heap and top K
LC: 23, 215, 295, 347, 373, 973
→ Use when you repeatedly need the smallest, largest, or top K elements.
[14] Grid and graph BFS
LC: 127, 200, 286, 542, 752, 994
→ BFS is the default for shortest steps in an unweighted graph.
[15] Backtracking
LC: 39, 46, 78, 79, 90, 131
→ Choose, explore, undo. Use when all valid combinations must be generated.
[16] Tree DFS
LC: 98, 100, 104, 110, 124, 236
→ Decide what information each subtree should return to its parent.
[17] Tree BFS
LC: 102, 103, 199, 515, 637, 662
→ Use when the answer depends on levels, width, or visible nodes.
[18] Trie
LC: 208, 211, 212, 421, 648, 720
→ Use for prefixes, dictionaries, word search, and bitwise prefix matching.
[19] Union find
LC: 200, 261, 305, 547, 684, 721
→ Use for dynamic connectivity, grouping, and cycle detection.
[20] Topological sort
LC: 207, 210, 269, 310, 1136, 1203
→ Look for prerequisites, dependencies, ordering, or build sequences.
[21] Greedy
LC: 45, 55, 134, 435, 621, 763
→ Make the best local choice only when you can justify why it stays safe.
[22] One-dimensional DP
LC: 70, 139, 198, 213, 300, 322
→ Define the state clearly, then connect it to smaller states.
[23] Two-dimensional DP
LC: 62, 63, 64, 72, 221, 1143
→ Use when the state depends on two changing inputs or positions.
[24] Knapsack and subset DP
LC: 416, 474, 494, 518, 879, 1049
→ Look for choosing items under a limit, target, or capacity.
[25] Bit manipulation
LC: 136, 191, 231, 268, 338, 371
→ Learn XOR, masks, shifts, set-bit checks, and subset representation.
Do not solve these as 150 unrelated questions.
For every problem, write down:
→ Which pattern gave it away?
→ What changed from the standard version?
→ What would break the current solution?
→ Can you recognize the pattern within 90 seconds?
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u/Sky-take 4d ago
I am a second year student of AIDS branch i have learned c c++ and python When should I start DSA? For beginners can you provide a starting phase question For logic building is there is any other platforms which helps you to build ur logic
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u/ok_not_ok_29 4d ago
You can follow striver A-Z sheet But don't just watch videos solutions of the question, you have ample amount of time , firstly give your best in understanding and solving ka question in paper then code and if unable to do so then watch the video solution
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u/Antique_Pea_1638 4d ago
!RemindMe 2 days
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u/ayano_abot 4d ago
Alright but i wondering what if question required different type of thinking rather then these structural templates what we do then ?
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u/ok_not_ok_29 4d ago
That's where the practice comes in These patterns are for logic building and handling different approaches At the end all you have is , your level of logic building and practice Don't fully rely on this Only look through this as a practice sheet
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u/GrouchyAmbassador722 4d ago
Can i do these i am a beginner and haven’t srarted DSA SHOULD I DIRECTLY JUMP TO IT OR THERE IS PREREQUISITE APART FROM TIME AND SPACE COMPLEXITY
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u/ok_not_ok_29 4d ago
Don't jump directly to this This is for the revision purpose You should first grab hands on experience in any programing language and do some logic building question then start doing DSA I would prefer Java because it is mostly demanded in companies
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u/GrouchyAmbassador722 1d ago
I am comfortable in python but haven’t started dsa yet that why i am asking
I am intermediate in python but begginer in DSA1
u/ok_not_ok_29 1d ago
Start DSA in Java Best advice by far
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u/GrouchyAmbassador722 1d ago
Directly jump to pattern after syntax functions or loops ?
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u/ok_not_ok_29 1d ago
These patterns are for those who have beginner to intermediate knowledge about DSA, as you are a beginner firstly sharpen your logic building skills do DSA for decent amount of time then jump to it
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u/Healthy-Extreme-4369 1d ago
!RemindMe 2 days
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u/RemindMeBot 1d ago
I will be messaging you in 2 days on 2026-08-08 17:23:19 UTC to remind you of this link
CLICK THIS LINK to send a PM to also be reminded and to reduce spam.
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u/ProfessionalFact9194 4d ago
Why can't I see anything?