What others already mentioned. C#'s main has code copy-pasta from C++ and is not a valid C# code, so can't build in C#.

So much for hacker ranking and leet coding :lol:

Here is my c++ solution you watch vide explanation here : https://youtu.be/COnfpdhOlN8

SinglyLinkedListNode* insertNodeAtHead(SinglyLinkedListNode* llist, int data) {
   SinglyLinkedListNode* new_node = new SinglyLinkedListNode(data);
   new_node -> next = llist;
   return new_node;
}

SinglyLinkedListNode* insertNodeAtHead(SinglyLinkedListNode* head, int val) { SinglyLinkedListNode* temp = new SinglyLinkedListNode(val); temp->next = head; return temp; }

c# Main() method is broken, cannot fix it it is locked for editing.

The c# method has error here :: PrintSinglyLinkedList(llist->head, "\n", textWriter);

The -> operator is not allowed c# (pointer only for c/c++).

Use another compiler.