## LeetCode - 236. Lowest Common Ancestor of a Binary Tree

## Problem Statement

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**).”

Given the following binary tree: root = [3,5,1,6,2,0,8,null,null,7,4]

*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.
```

## Solution

```
func lowestCommonAncestor(root, p, q *TreeNode) *TreeNode {
if root == nil {
return nil
}
if root == p || root == q {
return root
}
left := lowestCommonAncestor(root.Left, p, q)
right := lowestCommonAncestor(root.Right, p, q)
if left != nil && right != nil {
return root
}
if left == nil {
return right
}
if right == nil {
return left
}
return nil
}
```