Find the Closest Value in a Binary Search Tree

# Find the Closest Value in a Binary Search Tree A binary search tree is supplied in level-order form, using null for a missing child. Find the stored integer whose numeric value is closest to a floating-point target. Use the BST ordering rather than requiring a full traversal. ### Function Signature ```text closest_bst_value(tree: list[int | null], target: float) -> int ``` ### Valid Input Domain The list encodes one nonempty valid BST with unique integer values. Null entries denote absent children. Inputs guarantee exactly one closest stored value. ### Exact Output Semantics Return the unique integer value minimizing absolute(value - target). Because the valid domain guarantees uniqueness, no tie-break is needed. ### Constraints - 1 <= number of non-null nodes <= 100,000. - -10^9 <= node value <= 10^9. - -10^9 <= target <= 10^9. - The tree representation contains no unreachable non-null entries. ### Public Examples #### Example 1 Input: tree = [4, 2, 5, 1, 3], target = 3.714 Output: 4 Four is closer to 3.714 than any other stored value. #### Example 2 Input: tree = [2, 1, 3], target = 1.2 Output: 1 One is the unique closest value. ### Hints - At every visited node, compare its value with both the current best and the target. - The BST ordering tells you which unexplored side can still contain a closer value.