The precedence part is what trips people up.
Use a stack to handle operator precedence by evaluating multiplication and division immediately, while deferring addition and subtraction. Parse the expression token by token, maintaining a current number and a sign, and push intermediate results onto the stack. Finally, sum the stack to get the result.
Pro tip: Clarify edge cases upfront, such as division by zero and integer overflow, and mention that you'd handle them gracefully (e.g., throw an exception or use long). Also, discuss the time and space complexity: O(n) time and O(n) space, but note that space can be O(1) with a two-pass approach if needed.
Confirm the input format, operator precedence, integer division truncation, and handling of division by zero or overflow. Ask if the expression is guaranteed valid and if negative numbers can appear as intermediate results.
Decide between a stack-based single-pass approach or a two-pass approach (first handle * and /, then + and -). Explain why stack is suitable for deferring addition/subtraction.
Describe the step-by-step process: initialize stack, current number, and sign; iterate through tokens; for * and /, pop and compute; for + and -, push; finally sum stack. Use a concrete example to illustrate.
State time complexity O(n) and space complexity O(n) for stack, but mention that space can be reduced to O(1) with a two-pass approach. Discuss trade-offs between simplicity and memory.
Mention testing with expressions like '3+2*2', ' 3/2 ', ' 3+5 / 2 ', and cases with division by zero or large numbers to ensure correctness.
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