Use the BST property to guide a search toward the target, keeping track of the closest value seen so far. At each node, update the closest if the current node is nearer to the target, then move left if the target is smaller or right if larger. Continue until you reach a null child, returning the closest value.
Pro tip: Mention that the iterative approach uses O(1) space and avoids recursion overhead, which is often preferred in production code. Also, clarify how you handle ties (e.g., if two nodes are equally close, return either or specify a rule).
Confirm that the BST is non-empty, the target can be any number (including outside the range of values), and ask if ties should be broken in a specific way.
Set a variable to store the closest value, initially the root's value, and a pointer to traverse the tree starting at the root.
While the current node is not null, compare the absolute difference between the node's value and the target with the current closest difference; update the closest if the node is closer. Then move left if the target is less than the node's value, otherwise move right.
Once the traversal ends (current node becomes null), return the stored closest value.
State that the time complexity is O(h) where h is the height of the tree (O(log n) for balanced BST, O(n) worst-case), and space complexity is O(1) for the iterative approach.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.