235. Lowest Common Ancestor of a Binary Search Tree

#### QUESTION:

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 class Solution {
public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
if (root == null) return null;
if (root.val > p.val && root.val > q.val)
return lowestCommonAncestor(root.left, p, q);
if (root.val < p.val && root.val < q.val)
return lowestCommonAncestor(root.right, p, q);
return root;
}
}
``````
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