# Lowest Common Ancestor of a Binary Tree – Leetcode Solution

In this post, we are going to solve the 236. Lowest Common Ancestor of a Binary Tree problem of Leetcode. This problem 236. Lowest Common Ancestor of a Binary Tree is a Leetcode medium level problem. Let’s see the code, 236. Lowest Common Ancestor of a Binary Tree – Leetcode Solution.

## Problem

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

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 = [3,5,1,6,2,0,8,null,null,7,4], p = 5, q = 1
Output: 3
Explanation: The LCA of nodes 5 and 1 is 3.``````

### Example 2 :

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

### Example 3 :

``````Input: root = [1,2], p = 1, q = 2
Output: 1``````

### 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 tree.

Now, let’s see the code of 236. Lowest Common Ancestor of a Binary Tree – Leetcode Solution.

# Lowest Common Ancestor of a Binary Tree – Leetcode Solution

### 236. Lowest Common Ancestor of a Binary 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(root == null || root == p || root == q) return root;

TreeNode left = lowestCommonAncestor(root.left,p,q);
TreeNode right = lowestCommonAncestor(root.right,p,q);

if(left == null){
return right;
} else if(right == null){
return left;
}else{
return root;
}
}
}```

### 236. Lowest Common Ancestor of a Binary 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 || root == p || root == q) return root;
TreeNode* left = lowestCommonAncestor(root->left, p, q);
TreeNode* right = lowestCommonAncestor(root->right, p, q);
return !left ? right : !right ? left : root;
}
};```

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

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

class Solution(object):
def lowestCommonAncestor(self, root, p, q):
if root in (None, p, q): return root
left, right = (self.lowestCommonAncestor(kid, p, q)
for kid in (root.left, root.right))
return root if left and right else left or right
```

Note: This problem 236. Lowest Common Ancestor of a Binary Tree is generated by Leetcode but the solution is provided by CodingBroz. This tutorial is only for Educational and Learning purpose.