C++ cyclic dependency confusion with adjacency list representation

Sorry for my inexperience with C++, but I spent quiet some time with solving a cyclic dependency issue and hence posing this.

I am trying to represent a Adjacency List in C++.

I have struct Node,

struct Node{

    int data;
    unordered_set<Node, Hash> links;

    bool operator == (Node const& other) const{
        return (data == other.data);
    }

    Node(){
    }

    Node(int data){
        this->data = data;
    }
};

and I have my Hash functor

struct Hash {
    size_t operator()(const Node &node) const {
        return node.data;
    };
};

I noticed that Hash uses Node and Node uses Hash

If for the purpose of this exercise I want to declare everything in a single file, which one should I declare first.

I tried forward declaration of both Hash and Node with defining either of them first, but none of them compiled.

PS: This is not homework, I'm trying to solve graph algorithm puzzles online