Problem database last updated: June 20, 2025
4 problems · 0 Easy, 1 Medium, 3 Hard · Ranked #291 of 458
0 Easy
0% · avg 23%
1 Medium
25% · avg 59%
3 Hard
75% · avg 18%
Based on 4 reported problems, Fastenal interviews are significantly harder than average - 75% Hard vs 18% across all companies.
Compared to the industry average, Fastenal puts unusual emphasis on string (100% of problems, 3.6x the industry average), hash-table (75% of problems, 3.3x the industry average). If you're short on time, these are the categories to double down on.
The most common topics are string (100%), hash-table (75%), sliding-window (25%), stack (25%). Problems below are sorted by frequency, the ones at the top are asked most often.
| Problem | Difficulty | Frequency | Topics | |
|---|---|---|---|---|
Minimum Window Substring Given two strings s and t of lengths m and n respectively, return the minimum window substring of s such that every character in t (including duplicates) is inc... | Hard | Very Likely | hash-tablestringsliding-window | Solve |
Number of Atoms Given a string formula representing a chemical formula, return the count of each atom. | Hard | Very Likely | hash-tablestringstack | Solve |
Sum of Beauty of All Substrings The beauty of a string is the difference in frequencies between the most frequent and least frequent characters. | Medium | Very Likely | hash-tablestringcounting | Solve |
Last Substring in Lexicographical Order Given a string s, return the last substring of s in lexicographical order. | Hard | Very Likely | two-pointersstring | Solve |
Minimum Window Substring
SolveGiven two strings s and t of lengths m and n respectively, return the minimum window substring of s such that every character in t (including duplicates) is inc...
Number of Atoms
SolveGiven a string formula representing a chemical formula, return the count of each atom.
Sum of Beauty of All Substrings
SolveThe beauty of a string is the difference in frequencies between the most frequent and least frequent characters.
Last Substring in Lexicographical Order
SolveGiven a string s, return the last substring of s in lexicographical order.
Frequency scores are based on crowdsourced interview reports. A higher score means the problem has been reported more often in recent Fastenal interviews.
Very Likely
75-100%
Likely
50-74%
Sometimes
25-49%
Rare
0-24%
Fastenal interviews focus heavily on string, hash-table, sliding-window problems. If you're short on time, these are the categories to prioritize. The problems on this page are sorted by frequency, so start from the top and work your way down.
Beyond solving problems, practice explaining your approach. Fastenal interviewers care about your thought process - how you break down a problem, consider edge cases, and evaluate tradeoffs between solutions. A clean O(n) solution you can explain clearly beats an O(log n) solution you can't articulate.
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Fastenal has been reported to ask 4 distinct coding problems. The most common topics are string, hash-table, sliding-window. 0 are Easy difficulty, 1 are Medium, and 3 are Hard. Problems are sorted by frequency - the ones at the top are asked most often.
Based on 4 reported problems, Fastenal interviews are significantly harder than average - 75% Hard vs 18% across all companies. 25% of questions are Medium difficulty. Focus on the high-frequency Medium problems first, then work through the Hard ones.
Start with the highest-frequency problems listed on this page. Focus on the core topics: string, hash-table, sliding-window. Practice solving them under time pressure and explaining your approach out loud. Mock interviews with AI can simulate the real experience.
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