BFS with a column tracker is the move here.
Use a BFS traversal while tracking each node's column index, storing nodes in a map from column to list of values. Then sort the columns and output the lists, ensuring within each column nodes are ordered by depth (top-to-bottom) and for same depth, left-to-right.
Pro tip: Clarify the tie-breaking rule for nodes in the same column and depth: if the problem expects left-to-right order, BFS naturally preserves that; otherwise, you may need to sort by value. Mentioning this nuance shows attention to detail.
Confirm the ordering rules: top-to-bottom by depth, and for same depth, left-to-right. Discuss edge cases like empty tree, single node, and nodes with same column and depth.
Use BFS with a queue storing (node, column, depth) to process level by level. Use a hash map to group nodes by column, and within each column, maintain order by depth and left-to-right.
During BFS, for each node, append its value to the list for its column. Since BFS processes nodes level by level, nodes at the same depth are added left-to-right, preserving the required order.
After traversal, sort the column keys in ascending order and concatenate the lists to form the final result.
State time complexity O(N log N) due to sorting columns (or O(N) if using ordered map), space O(N). Walk through a small example to verify correctness.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
Clarify assumptions (e.g., valid input, no spaces, division by zero) and then propose a two-pass stack-based solution: first pass handles * and /, second pass handles + and -. Walk through an example to demonstrate correctness and discuss time/space complexity.
Pro tip: Mention that you can optimize space by using a running result and last operand instead of a full stack, and explicitly handle integer division truncation toward zero (e.g., using Math.trunc in JavaScript or int() in Python).
Ask about input constraints (e.g., spaces, invalid expressions, division by zero) and confirm that integer division truncates toward zero. Discuss how to handle negative intermediate results.
Propose a two-pass stack-based method: first pass evaluates * and /, second pass evaluates + and -. Alternatively, use a single pass with a stack and a variable for the last operator.
Trace the algorithm on a sample expression like '3+2*2' to show how the stack evolves and how precedence is respected. Highlight how division truncation is applied.
State that time complexity is O(n) and space is O(n) for the stack. Mention that space can be reduced to O(1) by using a running result and last operand.
Discuss handling of multi-digit numbers, leading/trailing spaces, and division by zero. Suggest writing unit tests for expressions like '14-3/2' and '0-1'.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.