String Parsing, Tokenization, And Validation
Asked of: Software Engineer
Last updated

What's being tested
String parsing under strict format rules: splitting input into meaningful tokens while rejecting malformed cases early. Interviewers probe whether you can combine tokenization, validation, and simple data structures like stacks without losing edge cases around whitespace, signs, overflow, or delimiters.
Patterns & templates
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Single-pass lexer — scan with index
i, emit tokens, validate state transitions;O(n)time,O(1)orO(n)space. -
Parser state machine — track expected token type: number, operator, bracket, word, or end; catches
1++2,+1, and trailing operators. -
Safe integer accumulation — build numbers digit by digit using bounds checks before
value = value * 10 + digit; enforce 32-bit range. -
Stack matching for brackets — push opening chars, pop on closing chars, compare via map;
O(n)time,O(n)worst-case space. -
Whitespace-preserving tokenization — separate word tokens from space runs; reverse only words or rebuild with original spacing rules.
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Two-pointer in-place string/array edits — compact, reverse, or swap segments without extra copies; watch mutable vs immutable language constraints.
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Backtracking subsets — sort first for duplicate handling, recurse with
startindex; skip duplicates usingif i > start && nums[i] == nums[i-1].
Common pitfalls
Pitfall: Treating parsing as
split()only; strict validators usually require character-level control over empty tokens, leading zeros, signs, and spaces.
Pitfall: Checking overflow after arithmetic; in fixed-width languages, validate before multiply/add to avoid undefined or wrapped results.
Pitfall: Normalizing whitespace accidentally when the requirement says preserve original spaces, tabs, or relative spacing positions.
Practice these
The practice cards below cover the canonical variants — solve all of them and time yourself.
Featured in interview prep guides
Practice questions
- Reverse Words While Preserving SpacesBytedance · Software Engineer · Technical Screen · medium
- Build a validated add-sub calculatorBytedance · Software Engineer · Onsite · medium
- Solve these string, subset, and date problemsBytedance · Software Engineer · Technical Screen · medium
- Validate a bracket stringBytedance · Software Engineer · Technical Screen · medium
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