Is Split BST easy or hard?

Split BST is generally classified as a medium-level problem. The recursion logic is straightforward once you recognize that the BST property allows you to split subtrees without scanning the entire structure repeatedly.

Split BST Python/Java solution

The typical Python or Java solution uses a recursive helper function that returns two subtree roots. Depending on the comparison between node.val and V, the function splits either the left or right subtree and reconnects nodes accordingly.

How to solve Split BST in O(n)?

Traverse the tree recursively and compare each node's value with the target V. If the value is V, split the left subtree and attach the > portion back to node.left. This ensures every node is processed once.

What is the best approach for Split BST?

The recursive BST split is the most efficient and commonly expected solution. It uses the binary search tree ordering to decide whether each node belongs in the V tree. Each node is processed once, resulting in O(n) time and O(h) space where h is the tree height.

Is Split BST asked at Google/Amazon/Meta?

Split BST is a common tree manipulation problem that appears in interviews at companies like Google, Amazon, and Meta. It tests understanding of binary search tree properties, recursion, and pointer manipulation.

What data structure is used in Split BST?

The primary data structure is a Binary Search Tree. The solution relies on BST ordering properties along with recursion to partition nodes while preserving the original tree structure.

What is the time complexity of Split BST?

The optimal solution runs in O(n) time because each node in the tree is visited exactly once during the recursive split. Space complexity is O(h) due to the recursion stack, where h is the height of the binary search tree.

Description Hints 1 Solution Video 6:33

776. Split BST

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Given the root of a binary search tree (BST) and an integer target, split the tree into two subtrees where the first subtree has nodes that are all smaller or equal to the target value, while the second subtree has all nodes that are greater than the target value. It is not necessarily the case that the tree contains a node with the value target.

Additionally, most of the structure of the original tree should remain. Formally, for any child c with parent p in the original tree, if they are both in the same subtree after the split, then node c should still have the parent p.

Return an array of the two roots of the two subtrees in order.

Example 1:

Input: root = [4,2,6,1,3,5,7], target = 2
Output: [[2,1],[4,3,6,null,null,5,7]]

Example 2:

Input: root = [1], target = 1
Output: [[1],[]]

Constraints:

The number of nodes in the tree is in the range [1, 50].
0 <= Node.val, target <= 1000

Asked at 2 companies

Coupang Amazon

Topics

Hints open one at a time

Hint 1

Use recursion. If root.val <= V, you split root.right into two halves, then join it's left half back on root.right.

6:33

Still stuck?Read the written solution, or watch a walkthrough.

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