# Lowest Common Ancestor of a Binary Search Tree – Leetcode Solution

In this post, we are going to solve the 235. Lowest Common Ancestor of a Binary Search Tree problem of Leetcode. This problem 235. Lowest Common Ancestor of a Binary Search Tree is a Leetcode easy level problem. Let’s see code, 235. Lowest Common Ancestor of a Binary Search Tree – Leetcode Solution.

## Problem

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: “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).”

### 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.
``````

### 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, 105]`.
• `-109 <= Node.val <= 109`
• All `Node.val` are unique.
• `p != q`
• `p` and `q` will exist in the BST.

Now, let’s see the code of 235. Lowest Common Ancestor of a Binary Search Tree – Leetcode Solution.

# Lowest Common Ancestor of a Binary Search Tree – Leetcode Solution

### 235. Lowest Common Ancestor of a Binary Search Tree – Solution in Java

```/**
* Definition for a binary tree node.
* public class TreeNode {
*     int val;
*     TreeNode left;
*     TreeNode right;
*     TreeNode(int x) { val = x; }
* }
*/

class Solution {
public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
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;
}
}
}```

### 235. Lowest Common Ancestor of a Binary Search Tree – Solution in C++

```/**
* Definition for a binary tree node.
* struct TreeNode {
*     int val;
*     TreeNode *left;
*     TreeNode *right;
*     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/

class Solution {
public:
TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
if (root == NULL) return NULL;
if (p->val < root->val and q->val < root->val){
return lowestCommonAncestor(root->left, p, q);
}
else if (p->val > root->val and q->val > root->val){
return lowestCommonAncestor(root->right, p, q);
}
return root;
}
};```

### 235. Lowest Common Ancestor of a Binary Search Tree– Solution in Python

```# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
def lowestCommonAncestor(self, root: 'TreeNode', p: 'TreeNode', q: 'TreeNode') -> 'TreeNode':
if root:
if root.val > p.val and root.val > q.val:
return self.lowestCommonAncestor(root.left, p, q)
elif root.val < p.val and root.val < q.val:
return self.lowestCommonAncestor(root.right, p, q)
else:
return root
```

Note: This problem 235. Lowest Common Ancestor of a Binary Search Tree is generated by Leetcode but the solution is provided by CodingBroz. This tutorial is only for Educational and Learning purpose.