Question

I’m making a C++ Maze program using disjoint sets and the Union/Find operations.

I have a MakeSet(int x) function which creates a new Node for every integer element x in the maze. (i.e 1 to 16 for a 4×4 maze). Thus initially every element is in its own set.

My MakeSet looks like this

void Maze::MakeSet(int x)
{
    Node *root = new Node;
    root->label = x;
    root->parent = NULL;
}

But in the CreateMaze() function I have to call MakeSet many times to get all the elements into their own set initially. Thus, the root will keep being overwritten. How do I dynamically allocate many different nodes? Should I keep them separated in an array?

Answer 1

You already allocate a new Node, you are just not keeping it. You need to change the function to return Node*, and store the results in an array or a vector.

Node* Maze::MakeSet(int x) {
    Node *root = new Node;
    root->label = x;
    root->parent = NULL;
    return root;
}

Node *nodes[16];
for (int i = 0 ; i != 16 ; i++) {
    nodes[i] = Maze::MakeSet(i);
}

An even better approach would be to do Node initialization in a constructor:

Node::Node(int x) : label(x), parent(NULL) {
}

You can now create all sets in a loop, and store pointers to them in an array:

Node *nodes[16];
for (int i = 0 ; i != 16 ; i++) {
    nodes[i] = new Node(i);
}