# Description

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 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).”

``````         _______3______
/              \
___5__          ___1__
/      \        /      \
6      _2       0       8
/  \
7   4
``````

For example, the lowest common ancestor (LCA) of nodes 5 and 1 is 3. Another example is LCA of nodes 5 and 4 is 5, since a node can be a descendant of itself according to the LCA definition.

The original problem is here.

The original code is here.

# My Solution

I solve this problem in C++, as below:

``````/*
*Lowest Common Ancestor of a Binary Tree
*Author: shuaijiang
*Email: zhaoshuaijiang8@gmail.com
*/
#include<iostream>
#include<stack>
#include<stdlib.h>
using namespace std;

/**
* 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 (root == p || root == q) return root;
TreeNode *L = lowestCommonAncestor(root->left, p, q);
TreeNode *R = lowestCommonAncestor(root->right, p, q);
if (L && R) return root;
return L ? L : R;
}
};
``````

# Note

To solve the problem, recursion is needed.