# Leetcode 236 Solution

This article provides solution to leetcode question 236 (lowest-common-ancestor-of-a-binary-tree)

https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-tree

## Solution

``````/**
* 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 {
TreeNode* m_res;
public:
int findLowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
if (root == 0)
return 0;

int root_cnt = 0;

if (root == p || root == q)
root_cnt = 1;

int left_cnt = findLowestCommonAncestor(root->left, p, q);
int right_cnt = findLowestCommonAncestor(root->right, p, q);

if ((left_cnt == 1 && right_cnt == 1) || (root_cnt == 1 && left_cnt + right_cnt == 1))
m_res = root;

return root_cnt + left_cnt + right_cnt;
}

TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
findLowestCommonAncestor(root, p, q);

return m_res;
}
};
``````