I went with BFS and grabbed the last node of each level, which worked fine.
Use BFS level-order traversal, recording the last node at each level. Alternatively, use DFS prioritizing the right child, tracking depth to capture the first node seen at each new depth. Both approaches yield O(n) time and O(h) space.
Pro tip: Clarify that the right side view is the set of rightmost nodes at each depth, not just nodes on the rightmost path. Mention that BFS is more intuitive but DFS uses less memory for skewed trees.
Confirm that the right side view includes the rightmost node at each depth, even if it's not on the rightmost path. Discuss edge cases like empty tree or single node.
Decide between BFS (level-order) and DFS (right-first). Explain the trade-offs: BFS is straightforward, DFS can be more space-efficient for deep trees.
Use a queue to process nodes level by level. For each level, record the last node's value. Enqueue left and right children for the next level.
Traverse right child first, then left. Keep track of the current depth and add the node's value to the result if it's the first time visiting that depth.
State that both approaches run in O(n) time and O(h) space, where h is the tree height. For BFS, space is O(w) where w is the maximum width.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
BFS with a (node, col) queue and a defaultdict felt natural once I started writing it.
Use a BFS or DFS traversal while tracking each node's horizontal distance (column) from the root. Store nodes in a hash map keyed by column, then output columns in sorted order, sorting nodes within each column by depth and value as needed.
Pro tip: Clarify upfront whether nodes in the same column should be ordered by depth (top-to-bottom) and then by value, as Meta often expects this tie-breaking. Mention that you can avoid sorting columns by tracking min/max column indices during traversal.
Ask about tie-breaking rules (depth vs. value), whether to include empty columns, and how to handle a null root. Confirm the expected output format.
Select BFS (level-order) or DFS (preorder) to traverse the tree. Use a hash map mapping column index to a list of nodes, and track min/max column indices.
During traversal, compute each node's column (root = 0, left = parent-1, right = parent+1). Append the node's value to the map entry for that column, along with its depth if needed for sorting.
Sort columns from min to max. For each column, sort nodes by depth (and value if required). Collect the values into the final list of lists.
State time and space complexity (O(n log n) if sorting, O(n) with BFS and ordered map). Walk through a small example and edge cases like skewed trees.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
Explain that a single BFS pass can capture both views by tracking the first and last node at each level. Use a queue for level-order traversal and record the first node as the left view and the last node as the right view.
Pro tip: Mention that this approach is optimal in time and space, and clarify that the left view is not simply the left child of each node but the leftmost node at each depth.
Confirm that the left view consists of the first node at each level and the right view consists of the last node at each level. Discuss edge cases like empty tree or single node.
Describe using a queue to perform level-order traversal. For each level, process all nodes, and while processing, note the first and last node encountered.
Initialize an empty queue and enqueue the root. While the queue is not empty, determine the level size, then iterate through the level: for the first node, add to left view; for the last node, add to right view. Enqueue children of each node.
State that time complexity is O(n) since each node is visited once, and space complexity is O(w) where w is the maximum width of the tree, due to the queue.
Mention that separate DFS or BFS passes could work but would be less efficient. Emphasize that the single BFS pass is optimal and elegant.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.