Use a stack-based approach to evaluate the expression in a single pass, handling operator precedence by deferring addition and subtraction until after processing multiplication and division. Alternatively, use a two-pass approach: first parse and compute all multiplication/division, then sum the results. Clearly explain your choice and walk through an example.
Pro tip: Mention that you can solve it without a stack by keeping a running total and a last value for handling precedence, which saves space. Also, discuss how to handle edge cases like negative numbers and spaces.
Confirm that the expression contains non-negative integers, +, -, *, /, and spaces, and that division truncates toward zero. Ask if there are any constraints on the input size or if parentheses are included (they are not in this problem).
Decide between a stack-based single-pass solution or a two-pass approach. Explain that the stack approach handles operator precedence by pushing numbers and applying * and / immediately, while + and - are pushed as signed numbers.
Describe initializing a stack, a current number, and an operator. Iterate through the string, building numbers, and when an operator is encountered, apply the previous operator to the stack. At the end, sum the stack.
Discuss handling spaces, the last number, and negative results from subtraction. Mention that division should truncate toward zero, which in Python requires int(a / b) or a // b with adjustment for negatives.
State that the time complexity is O(n) and space complexity is O(n) for the stack, but can be O(1) with the running total approach. Mention that the input is processed once.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
They said no need to write code which felt like a relief until I actually had to explain it out loud.
First, clarify the original problem and the role of parentheses in it. Then, explain how to extend the solution by incorporating a stack to handle nested parentheses, and discuss how this affects the algorithm's time and space complexity. Finally, mention edge cases and potential trade-offs.
Pro tip: Demonstrate awareness of real-world applications, such as parsing expressions in OtterAI's transcription or natural language processing, to show you understand the broader impact of the change.
Restate the original problem to ensure you and the interviewer are aligned on the context and constraints.
Explain how parentheses introduce nesting and grouping, which likely requires tracking state or using a stack.
Describe the modification: e.g., use a stack to push on '(' and pop on ')', and adjust the algorithm to handle the enclosed subproblem.
Discuss how time and space complexity change, and any trade-offs between different approaches (e.g., recursion vs. stack).
Mention handling of unbalanced parentheses, empty parentheses, and nested structures, and how to test these cases.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.