remove duplicates from an unsorted linked list

more fun with algorithms: how to remove duplicates from an unsorted linked list in cpp?
easy - just walk along the list and delete duplicate items.
but how to know an item is a duplicate?
well, for every item we could scan the list from the beginning, but this is a ridiculously naive solution - how about keeping all values we encounter while iterating and checking if we have already met a current value?
putting those in an unordered set would be good enough i'd say

#include 
#include 
using namespace std;

struct List {
 int data = 0;
 List* next = nullptr;
 List(int x) : data(x) {}
};

void remove_duplicates(List* head) {
 std::unordered_set cache;
 cache.insert(head->data);
 List* next = head->next;
 while (next != nullptr) {
  if (cache.count(next->data) > 0) {
   head->next = next->next;
   delete next;
   next = head->next;
  } else {
   cache.insert(next->data);
   head = next;
   next = head->next;
  }
 }
}

int main() {
 List* head = new List(1);
 List* list = head;
 for (int index = 2; index < 10; ++index) {
  List* next = new List(index);
  //a silly way to make duplicates in the list
  if (next->data % 2 == 0) {
   next->data = 2;
  } else if (next->data % 3 == 0) {
   next->data = 3;
  }
  list->next = next;
  list = next;
 }

 remove_duplicates(head);

 while (head != nullptr) {
  printf("%d\n", head->data);
  head = head->next;
 }

 return 0;
}

https://ideone.com/K19v5o