236. Lowest Common Ancestor of a Binary Tree.cpp

/**
 * 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 || 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;
        }
        
        if( right == NULL )
        {
            return left;
        }
        
        return root;
    }
};