The DSA Patterns Engineers Actually Fail: A First-Attempt Pass Rate Study

Across 2,909 engineers and 22,908 first-real-attempt solves on Thita.ai, the average DSA pattern is solved correctly on the first try only 39.6% of the time — and the hardest pattern, Two Pointers, is solved on the first try just 35.1% of the time. This is a first-of-its-kind, data-backed ranking of which DSA pattern families are actually hardest to get right on attempt one, straight from platform submission history rather than opinion or survey.

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Why "hardest" has never had real data behind it

Every "hardest LeetCode pattern" list on the internet is a ranked opinion — a mentor's gut feeling, a Reddit thread, a YouTuber's top 10. Nobody has published first-attempt pass-rate data at pattern granularity, because nobody outside a platform with real submission logs can. Thita.ai's code execution history gives us that data. This post publishes it, with the full methodology behind it linked at the bottom.

What "first-attempt pass rate" means here

For every (user, problem) pair with at least one real, executed submission, we look at that user's first graded submission for that problem and ask: was it accepted? The first-attempt pass rate for a pattern is the share of those first attempts that passed, rolled up across every problem mapped to that pattern. It is not the eventual pass rate (nearly everyone eventually solves a problem they stick with) — it is a measure of how often the pattern is understood correctly the first time it is applied.

We also report median attempts to first pass: among the pairs that eventually passed, how many real submissions it typically took.

Every number below is suppressed if fewer than 50 distinct users back it — full rule in the Methodology section and its own companion post.

The ranked table: hardest to easiest DSA patterns

15 of Thita's 16 DSA pattern families had enough distinct users (k≥50) to publish; Segment Tree & Fenwick Tree patterns did not have enough mapped submissions in this snapshot and are excluded rather than estimated.

Rank	Pattern	First-attempt pass rate	Median attempts to pass	n (users / problems)
1 (hardest)	Two Pointers	35.1%	2	1,988 users / 33 problems
2	Array/Matrix Manipulation	36.9%	2	491 users / 19 problems
3	Sliding Window	37.8%	2	500 users / 30 problems
4	String Manipulation	40.3%	2	230 users / 17 problems
5	Linked List Manipulation	41.1%	2	181 users / 16 problems
6	Heap (Priority Queue)	42.5%	2	184 users / 22 problems
7	Binary Search	43.3%	2	175 users / 26 problems
8	Tree Traversal (DFS & BFS)	45.0%	2	334 users / 33 problems
9	Design Patterns	45.7%	1	101 users / 36 problems
10	Stack Patterns	46.1%	2	240 users / 26 problems
11	Graph Traversal (DFS & BFS)	46.6%	1	254 users / 60 problems
12	Dynamic Programming	46.9%	1	212 users / 43 problems
13	Backtracking	48.4%	1	69 users / 19 problems
14	Greedy Patterns	50.0%	1	123 users / 16 problems
15 (easiest)	Bit Manipulation	53.9%	1	102 users / 8 problems

Overall, across all 404 mapped problems: a 39.6% first-attempt pass rate, over 22,908 (user, problem) pairs from 2,909 distinct users.

A pattern with a reputation as "advanced" — Dynamic Programming, Graph Traversal, Backtracking — actually clears the bar on the first try more often than Two Pointers or Sliding Window. The likely reason: DP and graph problems are usually approached slowly and deliberately (people expect them to be hard and plan before coding), while Two Pointers and Sliding Window problems look deceptively simple, so the first attempt is often a rushed guess at the invariant.

The hardest individual sub-patterns

Rolling up to 16 pattern families hides where the real difficulty concentrates. Of 100 tracked sub-patterns, 51 had enough users (k≥50) to publish. The 10 hardest:

Rank	Sub-pattern	Parent pattern	First-attempt pass rate	n users
1 (hardest)	Hashing – Frequency Map / Counting	Array/Matrix Manipulation	21.7%	143
2	Fixed Size (Subarray Calculation)	Sliding Window	25.4%	406
3	Merge Sorted Array (In-place from End)	Array/Matrix Manipulation	28.5%	288
4	Converging (Sorted Array Target Sum)	Two Pointers	29.6%	1,761
5	Graph BFS – Topological Sort (Kahn's Algorithm)	Graph Traversal	32.1%	78
6	Palindrome Check (Two Pointers / Reverse)	String Manipulation	32.2%	89
7	Plus One (Handling Carry)	Array/Matrix Manipulation	32.5%	147
8	String Reversal	Two Pointers	35.9%	400
9	Multiply Strings (Manual Simulation)	String Manipulation	36.4%	138
10	Merging Two Sorted Lists	Linked List Manipulation	36.8%	87

Converging (Sorted Array Target Sum) is the single most-attempted sub-pattern in the data (1,761 distinct users) and still clears the first-try bar under 30% of the time — the widest gap between "how common" and "how hard" in the whole study. The remaining 41 published sub-patterns, and full definitions for every field, are covered in the methodology post.

What this means for your prep

• Don't skip Two Pointers because it "looks easy." It has the lowest first-attempt pass rate of any pattern family in this data. Budget deliberate practice time on the Two Pointers pattern page, not just a quick review.
• Hashing and Array/Matrix sub-patterns deserve more respect than their reputation suggests. "Hashing – Frequency Map / Counting" is the single hardest sub-pattern measured, well below the pattern-level average for Array/Matrix Manipulation.
• Fixed-size sliding window is a common trap. Despite being taught as the "easy" sliding-window variant, it has the second-lowest first-attempt pass rate of any sub-pattern. Get the window-invariant logic solid on Sliding Window before moving to variable-size windows.
• Median attempts to pass is 2 for almost every pattern, meaning most engineers who eventually solve a problem needed one correction pass. If your first attempt fails, that is the median experience, not a red flag — the data says to debug and resubmit rather than switch approaches.
• Bit Manipulation, Greedy, and Backtracking cleared the first try most often in this data (53.9%, 50.0%, 48.4%) — useful patterns to lean on for early confidence-building before tackling Two Pointers or Sliding Window.

Methodology

Full detail — data sources, exact definitions, exclusions, and limitations — is in the companion methodology post. Summary:

• Data source: user_code_submissions (real, executed submissions only — UI states like analysis-only mode or missing-template runs are excluded) joined to each problem's primary pattern/subpattern mapping in technical_problem_subpattern_mappings.
• First attempt: each user's earliest real submission per problem, ordered by timestamp.
• Suppression: any pattern or sub-pattern cell backed by fewer than 50 distinct users is withheld from publication entirely (k-anonymity, stricter than the k=5 usual on this platform because this data is public).
• Snapshot date: 2026-09-07. Underlying counts: 22,908 (user, problem) pairs, 2,909 distinct users, 404 distinct problems.
• Cadence: this study is re-run quarterly.

Never published: submitted code, error messages, per-user data, or anything below the suppression threshold.

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Practice the patterns this data says are actually hardest — with instant AI code feedback on every attempt — on Thita.ai's DSA patterns course.