TreeNode* flatten_helper(TreeNode* root)
{
cout << root->val << endl;
if (root->left == NULL && root->right == NULL) return root;
if (root->left == NULL) return flatten_helper(root->right);
auto tmp = root->right;
root->right = root->left;
root->left = NULL;
auto leftEndNode = flatten_helper(root->right);
if (tmp != NULL)
{
leftEndNode->right = tmp;
return flatten_helper(tmp);
}
return leftEndNode;
}
static constexpr decltype(auto) apply(Xs&& xs) {
using Raw = typename detail::std::remove_reference<Xs>::type;
constexpr detail::std::size_t len = ::std::tuple_size<Raw>::value;
return flatten_helper(detail::std::forward<Xs>(xs),
detail::std::make_index_sequence<len>{});
}
void flatten(TreeNode* root)
{
if (root == NULL) return;
flatten_helper(root);
}
