My first instinct was to just do a full traversal and add up whatever fits, which works fine.
Clarify the problem and constraints, then discuss a recursive DFS solution that traverses the tree and sums nodes within the range. Optimize by pruning subtrees when the current node's value is outside the range and the tree is a BST, but note that for a general binary tree, full traversal is required.
Pro tip: Always ask whether the tree is a binary search tree (BST) or a general binary tree; if it's a BST, you can prune branches to achieve O(log n) time in balanced cases, otherwise it's O(n). Mentioning this distinction shows you think about efficiency and edge cases.
Ask if the tree is a BST or a general binary tree, and confirm that the range is inclusive. Also check if the tree can be empty or if node values can be negative.
For a general binary tree, a simple DFS (preorder, inorder, or postorder) works. For a BST, you can prune subtrees based on the range to optimize.
Write a recursive function that traverses the tree, adding the node's value if it's within the range. For BST, only recurse left if node.val > low and right if node.val < high.
State the time and space complexity: O(n) time for general tree, O(log n) for balanced BST with pruning; O(h) space for recursion stack.
Walk through a few test cases: empty tree, all nodes in range, no nodes in range, and a mix. Verify the sum is correct.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.