/** * 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) 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) return r; else if(!r) return l; else return root; } };