result.push_back(root->val);
dfs(root->left);
dfs(root->right);

result.push_back(root->left->val);
dfs(root->right);
dfs(root->left);

result.push_back(root->left->val);
dfs(root->left);
dfs(root->right);

result.push_back(root->right->val);
dfs(root->right);
dfs(root->left);