#235

Lowest Common Ancestor of a Binary Search Tree

Medium
TreeDFSBinary Search TreeBinary Tree

Given a binary search tree (BST), find the lowest common ancestor (LCA) node of two given nodes in the BST.

According to the [definition of LCA on Wikipedia](https://en.wikipedia.org/wiki/Lowest_common_ancestor): "The lowest common ancestor is defined between two nodes `p` and `q` as the lowest node in `T` that has both `p` and `q` as descendants (where we allow **a node to be a descendant of itself**)."

Examples

Example 1
Input: root = [6,2,8,0,4,7,9,null,null,3,5], p = 2, q = 8
Output: 6
The LCA of nodes 2 and 8 is 6.
Example 2
Input: root = [6,2,8,0,4,7,9,null,null,3,5], p = 2, q = 4
Output: 2
The LCA of nodes 2 and 4 is 2, since a node can be a descendant of itself according to the LCA definition.
Example 3
Input: root = [2,1], p = 2, q = 1
Output: 2

Constraints

  • •The number of nodes in the tree is in the range [2, 10^5].
  • •-10^9 <= Node.val <= 10^9
  • •All Node.val are unique.
  • •p != q
  • •p and q will exist in the BST.
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