Went iterative instead of trying to split the string recursively.
Clarify the grammar and constraints of the input string, then propose a recursive descent parser that evaluates expressions on the fly. Discuss handling of nested calls, numbers, whitespace, and error cases, and analyze time and space complexity.
Pro tip: Mention that you can avoid building an explicit AST by evaluating during parsing, which reduces memory overhead and simplifies the code. Also, proactively discuss edge cases like negative numbers, multi-digit numbers, and malformed input to show thoroughness.
Ask about the allowed function names, number formats (e.g., negative, decimals), whitespace, and error handling expectations. Confirm whether the input is guaranteed valid or if error handling is required.
Outline a simple grammar: expression = function '(' expression (',' expression)* ')' | number. Choose a recursive descent parser that evaluates as it parses, avoiding an explicit AST.
Write a function that scans the string, parses function names, arguments, and numbers, and recursively evaluates sub-expressions. Use an index pointer to track position and handle commas and parentheses.
Address malformed input, unknown functions, division by zero, and unexpected tokens. Decide whether to throw exceptions or return error codes, and discuss with the interviewer.
State that time complexity is O(n) where n is the string length, and space is O(d) for recursion depth. Walk through examples like 'add(1, sub(1, 0))' and test edge cases.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.