在C ++中递归填充N元树

Question

I'm attempting to create the game tree of the tic-tac-toe board game. I've written some basic methods, but I'm having trouble recursively populating the elements of the tree.

I'm using a Node struct to define the Nodes of the tree. Each node has an array of children.

struct node {
  string data;
  int height;
  node * child[9];
};

Each Node stores the content of a game board as a string. * is used to display blanks.

So, * * * * * * * * * would be a blank board.

I have a Tree class that implements the tree.

class Tree {
public:
  Tree();
  Tree(string data);
  ~Tree();

  void insert(string data, node * leaf);
  node * get_root();
  void populate(node * n);
  void generate_tree(node * n);
  int number_of_blanks(string);

private:
  void destroy_tree(node * leaf);

  node * root;
  node * temp;
  int count;
};

Tree::Tree(string data) {
  root = new node;
  root->data = data;
  root->height = 0;
  temp = root;
  count = 0;
}

Here is my method for inserting nodes. It inserts a new node to the first NULL child.

void Tree::insert(string data, node * leaf) {
  int i;
  //checks for first NULL child
  for(i = 0; i < 9; i++) {
    if(leaf->child[i] == NULL) {
      //first NULL child is inserted and all its children set to NULL
      leaf->child[i] = new node;
      leaf->child[i]->data = data;
      leaf->child[i]->height = leaf->height + 1;
      break;
    }
  }
}

This code works how I've intended it to, however I'm sure it's not the best method.

Where I'm having the most trouble is recursively populating the tree. My recursion either ends early, or is an endless loop. I'm not sure how to approach this problem, as I've never used recursion with a void method.

void Tree::generate_tree(node * leaf) {
  int i;
  string data;
  string player;
  int length = number_of_blanks(leaf->data);

  if(leaf->height % 2 == 0)
    player = "X";
  else
    player = "O";


  if(leaf->data.find_last_of('*',8) == string::npos) {
    cout << "This is a leaf!!!!!!!!! " << leaf->data << endl;
    return;
  }


  for(i = 0; i < length; i++) {
    if(leaf->height >=9 )
      return;
    data = leaf->data.replace(count,1,player);
    insert(data,leaf);
    cout << "New Node: " << data << " Height: " << leaf->child[i]->height << endl;
    count++;
    generate_tree(leaf->child[i]);
    count = 0;
  }
}

Any tips, or specific suggestions would be greatly appreciated. Thank you.

Answer 1

I'd recommend giving node a constructor and to initialize members before the code block that makes up the constructor. For example:

 node(string s, int h) : data(s), height(h) { 
     for (int i=0;i < 9; ++i) 
        child[i] = NULL; 
 }

Similarly for the constructor for Tree :

Tree::Tree(std::string data) : root(new node(data,0)), count(0) {}

This makes other parts of the code much simpler. For example, your insert code would now look like this:

void Tree::insert(std::string data, node * leaf) {
  //checks for first NULL child
  for(int i = 0; i < 9; i++) {
    if(leaf->child[i] == NULL) {
      //first NULL child is inserted and all its children set to NULL
      leaf->child[i] = new node(data, leaf->height+1);
      break;
    }
  }
}

I haven't had the time to analyze the rest, but this may make it easier for you to solve.