Lowest Common Ancestor of a Binary Search Tree

LCA of BST

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 v and w as the lowest node in T that has both v and w as descendants (where we allow a node to be a descendant of itself).”

        ______6______
       /              \
    ___2__          ___8__
   /      \        /      \
   0      _4       7       9
         /  \
         3   5

For example, the lowest common ancestor (LCA) of nodes 2 and 8 is 6. Another example is LCA of nodes 2 and 4 is 2, since a node can be a descendant of itself according to the LCA definition.

Solution:

public TreeNode lowestCommonAncestorBST(TreeNode root, TreeNode p, TreeNode q) {

        if(root == null) {
            return null;
        }
        if(p.val < root.val && q.val < root.val ) {
            return lowestCommonAncestor(root.left, p, q);
        }
        else if(p.val > root.val && q.val > root.val) {
            return lowestCommonAncestor(root.right, p, q);
        } else {
            return root;
        }

    }