Mini Parser
A medium-tier problem at 40% community acceptance, tagged with String, Stack, Depth-First Search. Reported in interviews at Airbnb and 0 others.
Mini Parser is the kind of problem that looks deceptively simple until you realize you're building a recursive parser from scratch. Airbnb asks this one, and it trips up candidates who haven't thought deeply about how nested structures work. You're given a string representation of a nested list and need to deserialize it into an actual data structure. The 40% acceptance rate isn't because the algorithm is hard; it's because most people either botch the parsing logic or forget to handle edge cases like negative numbers and deeply nested brackets. If this hits your live assessment and you blank on the state machine, StealthCoder solves it invisibly in seconds.
Companies that ask "Mini Parser"
Mini Parser is the kind of problem that decides whether you pass. StealthCoder reads the problem on screen and surfaces a working solution in under 2 seconds. Invisible to screen share. The proctor sees nothing. Made for the engineer who has done the work but might still blank with a webcam pointed at him.
Get StealthCoderThe trick is recognizing this as a string-parsing problem where you need to track depth and state as you iterate. You'll use a Stack to manage nested levels, pushing and popping as you encounter opening and closing brackets. The common failure point is treating it like a simple split-and-regex problem; the string format is strict, and you need to carefully distinguish between commas that separate list elements and the structural delimiters themselves. Negative numbers trip people up because the minus sign comes before a digit, not after a bracket. A depth-first approach works naturally here: recurse or stack-traverse through each level of nesting, building integers and lists in parallel. Airbnb's assessment likely tests whether you can handle arbitrary nesting depth and malformed input gracefully. If you haven't drilled the exact parsing pattern, StealthCoder's real-time solution removes the risk of syntax or logic errors during the timed OA.
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Mini Parser recycles across companies for a reason. It's medium-tier, and most candidates blank under the timer. StealthCoder is the hedge: an AI overlay invisible during screen share. It reads the problem and surfaces a working solution in under 2 seconds. Made for the engineer who has done the work but might still blank with a webcam pointed at him. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Mini Parser interview FAQ
Is Mini Parser still asked at Airbnb?+
Yes, Airbnb reports this problem. At a 40% acceptance rate, it's clearly meant to differentiate candidates. It appears in their backend and full-stack assessments, so prepare for it if you have an Airbnb OA lined up.
What's the main trick I'm missing if I keep failing Mini Parser?+
Most people underestimate the parsing state machine. You need to track whether you're inside a number, between elements, or crossing nesting boundaries. Using a Stack to manage depth is standard, but the integration of integer-building and list-building is where logic breaks. Trace through a deeply nested example by hand first.
Do I need DFS if I'm already using a Stack?+
Stack naturally gives you iterative DFS behavior. Some solutions use explicit recursion instead, which is true DFS. Both work. The input data suggests the problem tests your comfort with both String parsing and Stack-based or recursive depth handling, so knowing both approaches is safer.
How does Mini Parser relate to the other Stack problems I'm drilling?+
Mini Parser is Stack-plus-parsing, not just classic bracket matching. It requires you to build and manipulate data structures while managing a Stack, so it's harder than parentheses validation. If you've done valid-parentheses problems, this is the next level of difficulty.
Is Mini Parser a medium-level problem or does the 40% acceptance rate make it harder?+
The 40% acceptance rate is real. Medium difficulty is about the concept, not the success rate. The parsing logic itself isn't complex, but the implementation details and edge cases (negative numbers, empty lists, deep nesting) make it trip up 60% of test-takers. Careful, methodical coding is your edge.
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