二叉树的最大节点

TreeNode * (TreeNode * root) {
    
    if(root == NULL) return NULL;
    TreeNode *left=root;    
    TreeNode *right=root; 
    if(root->left !=NULL){
       left = maxNode(root->left);
    }
    if(root->right!=NULL){
       right= maxNode(root->right);
    }
    
    if (right->val>root->val)  
     root->val=right->val;
    if (left->val>root->val)  
     root->val=left->val;    
     return root;  
}