Tree-Based

“Tree-Based” is only a topic label, not enough information to code safely. Ask for the input representation, whether the structure is guaranteed acyclic, and the desired result. For a subtree computation, use postorder DFS and make the return contract precise, such as “the maximum value in this subtree” or “whether this subtree is valid.” For a path or level question, explain why preorder, postorder, or BFS fits. Never use node values as visited keys when duplicates are possible; use node identity for graph-like inputs. A standard full traversal is O(n) time, with O(h) call-stack space for DFS or O(w) queue space for BFS. Test null, a leaf, a completely skewed tree, and duplicate labels. This clarifying step is the correct answer until the interviewer provides a concrete property.