Trees

“Trees” is a category rather than a complete question. Ask whether the input is binary, n-ary, a BST, or an undirected adjacency list, and whether the desired result concerns order, paths, height, ancestors, or validation. Then explain a fitting primitive: DFS is good for subtree aggregation and root-to-leaf state; BFS is good for shortest unweighted depth and levels. State what each stack frame or queue entry represents before coding. A traversal over a valid tree visits n nodes in O(n) time. DFS uses O(h) stack space, potentially O(n) for a skewed tree; BFS uses O(w) queue space. Handle empty roots, leaves, duplicates, recursion depth, and whether parent pointers or cycles exist. Clarification is not avoidance: it prevents solving the wrong tree problem.