I knew the algorithm but explaining the 'why' behind each step while coding at the same time was harder than expected.
Start by clarifying the problem and edge cases, then explain the three-step algorithm: find the pivot (first decreasing element from the right), find the successor (smallest element greater than pivot to its right), and reverse the suffix. Emphasize that this achieves O(n) time and O(1) space, and discuss handling wrap-around and duplicates.
Pro tip: Mention that the algorithm is exactly what C++'s std::next_permutation uses, and that the reverse step is crucial for minimizing the suffix. Also, proactively discuss how to handle duplicates and the wrap-around case by reversing the entire array.
Restate the problem, confirm input/output format, and ask about edge cases like empty array, single element, duplicates, and wrap-around behavior.
Scan from right to left to find the first index i where nums[i] < nums[i+1]. If no such index exists, the array is in descending order, so reverse the entire array to get the smallest permutation.
From the right, find the first element nums[j] that is greater than nums[i]. Swap nums[i] and nums[j].
Reverse the subarray from i+1 to the end to get the smallest possible suffix, ensuring the next permutation is the immediate next in lexicographic order.
Explain that each step is O(n) time and O(1) space, and discuss edge cases: empty array, single element, all equal elements, and wrap-around.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
The division truncation toward zero tripped me up briefly.
Use a single left-to-right pass with a stack to handle operator precedence: accumulate terms for addition/subtraction, and for multiplication/division, apply the operator to the last term in the stack. This yields O(n) time and O(1) space if you use a running total and last term instead of a stack.
Pro tip: Clarify edge cases upfront: division truncation toward zero (e.g., -3/2 = -1), handling of spaces, and potential integer overflow. Also, mention that you can avoid a stack by maintaining a running sum and a last term, which keeps space constant.
Confirm input constraints: non-negative integers, operators +, -, *, /, no parentheses, spaces allowed. Ask about division truncation (toward zero) and integer overflow handling.
Decide between a stack-based approach (O(n) space) or a constant-space approach using a running total and last term. For Meta, aim for constant space to impress.
Iterate through the string, building numbers and applying operators. For + and -, push the signed number to the stack (or add to running total). For * and /, pop the last number, apply the operator, and push the result back.
Implement integer division that truncates toward zero (e.g., using Math.trunc or casting to int after division). Skip spaces during parsing.
Test with expressions like '3+2*2', ' 3/2 ', '3+5 / 2', and negative results. Verify O(n) time and O(1) space.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
Start by clarifying the current evaluator's design and assumptions, then propose a two-stack or recursive descent approach to handle parentheses and precedence. Explain how you would modify the tokenizer and parser to support nested expressions, and discuss trade-offs between different parsing strategies.
Pro tip: Mention that you would first check if the existing evaluator uses a simple left-to-right evaluation, and then highlight that adding parentheses often requires a shift to a proper parsing algorithm like shunting-yard or recursive descent, which also naturally handles precedence.
Ask about the existing evaluator's architecture: does it use a simple loop, a stack, or a parser? Understand its limitations with parentheses and precedence.
Decide between algorithms like shunting-yard (two stacks) or recursive descent. Consider factors like ease of implementation, extensibility, and performance.
Explain how the chosen algorithm processes parentheses (e.g., pushing/popping on stack or recursive calls) and enforces operator precedence (e.g., via precedence table or grammar rules).
Compare approaches in terms of time/space complexity, code complexity, and error handling (e.g., mismatched parentheses, invalid expressions).
Outline how you would test the extended evaluator with nested expressions and mixed operators, and mention potential optimizations or extensions.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.