Lowest Common Ancestor of a Binary Search Tree

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

According to the definition of LCA on Wikipedia: “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).”

Given binary search tree: root = [6,2,8,0,4,7,9,null,null,3,5]

Example 1:

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

Constraints:

• All of the nodes' values will be unique.

• p and q are different and both values will exist in the BST.

class Solution {
    public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
        if (root == null)
            return null;
        // If one node is on right and other on left, then this node is LCA
        if ((root.val > p.val && root.val < q.val) || (root.val < p.val && root.val > q.val))
            return root;
        // If we have not found a splitting node(LCA), then this node will be considered LCA
        if (root.val == p.val || root.val == q.val)
            return root;
        // If both nodes are greater that current node, we will search on right
        if (p.val > root.val && q.val > root.val)
            return lowestCommonAncestor(root.right, p, q);
        // Else we will search on left
        return lowestCommonAncestor(root.left, p, q);
    }
}