你好我正在写一个avl树，我有一个问题。我现在有一个root作为全局因为我在课堂上和在main中使用它，如何在没有全局的情况下编写它？
struct avl_node {
int data;
struct avl_node *left;
struct avl_node *right;
}*root;
class avlTree {
public:
int height(avl_node *temp)
{
int h = 0;
if (temp != NULL)
{
int l_height = height (temp->left);
int r_height = height (temp->right);
int max_height = max (l_height, r_height);
h = max_height + 1;
}
return h;
}
int diff(avl_node *temp)
{
int l_height = height (temp->left);
int r_height = height (temp->right);
int b_factor= l_height - r_height;
return b_factor;
}
avl_node *rr_rotation(avl_node *parent)
{
avl_node *temp;
temp = parent->right;
parent->right = temp->left;
temp->left = parent;
return temp;
}
avl_node *ll_rotation(avl_node *parent)
{
avl_node *temp;
temp = parent->left;
parent->left = temp->right;
temp->right = parent;
return temp;
}
avl_node *lr_rotation(avl_node *parent)
{
avl_node *temp;
temp = parent->left;
parent->left = rr_rotation (temp);
return ll_rotation (parent);
}
avl_node *rl_rotation(avl_node *parent)
{
avl_node *temp;
temp = parent->right;
parent->right = ll_rotation (temp);
return rr_rotation (parent);
}
avl_node* balance(avl_node *temp)
{
int bal_factor = diff (temp);
if (bal_factor > 1)
{
if (diff (temp->left) > 0)
temp = ll_rotation (temp);
else
temp = lr_rotation (temp);
}
else if (bal_factor < -1)
{
if (diff (temp->right) > 0)
temp = rl_rotation (temp);
else
temp = rr_rotation (temp);
}
return temp;
}
avl_node* insert(avl_node *root, int value)
{
if (root == NULL)
{
root = new avl_node;
root->data = value;
root->left = NULL;
root->right = NULL;
return root;
}
else if (value < root->data)
{
root->left = insert(root->left, value);
root = balance (root);
}
else if (value >= root->data)
{
root->right = insert(root->right, value);
root = balance (root);
}
return root;
}
void display(avl_node *ptr, int level)
{
int i;
if (ptr!=NULL)
{
display(ptr->right, level + 1);
printf("\n");
if (ptr == root)
cout<<"Root -> ";
for (i = 0; i < level && ptr != root; i++)
cout<<" ";
cout<<ptr->data;
display(ptr->left, level + 1);
}
}
void inorder(avl_node *tree)
{
if (tree == NULL)
return;
inorder (tree->left);
cout<<tree->data<<" ";
inorder (tree->right);
}
void preorder(avl_node *tree)
{
if (tree == NULL)
return;
cout<<tree->data<<" ";
preorder (tree->left);
preorder (tree->right);
}
void postorder(avl_node *tree)
{
if (tree == NULL)
return;
postorder ( tree ->left );
postorder ( tree ->right );
cout<<tree->data<<" ";
}
avlTree()
{
root = NULL;
}
};
int main()
{
int choice, item;
avlTree avl;
while (1)
{
cout<<"\n---------------------"<<endl;
cout<<"AVL Tree Implementation"<<endl;
cout<<"\n---------------------"<<endl;
cout<<"1.Insert Element into the tree"<<endl;
cout<<"2.Display Balanced AVL Tree"<<endl;
cout<<"3.InOrder traversal"<<endl;
cout<<"4.PreOrder traversal"<<endl;
cout<<"5.PostOrder traversal"<<endl;
cout<<"6.Exit"<<endl;
cout<<"Enter your Choice: ";
cin>>choice;
switch(choice)
{
case 1:
system("cls");
cout<<"Enter value to be inserted: ";
cin>>item;
root = avl.insert(root, item);
break;
case 2:
system("cls");
if (root == NULL)
{
cout<<"Tree is Empty"<<endl;
continue;
}
cout<<"Balanced AVL Tree:"<<endl;
avl.display(root, 1);
break;
case 3:
system("cls");
cout<<"Inorder Traversal:"<<endl;
avl.inorder(root);
cout<<endl;
break;
case 4:
system("cls");
cout<<"Preorder Traversal:"<<endl;
avl.preorder(root);
cout<<endl;
break;
case 5:
system("cls");
cout<<"Postorder Traversal:"<<endl;
avl.postorder(root);
cout<<endl;
break;
case 6:
exit(1);
break;
default:
system("cls");
cout<<"Wrong Choice"<<endl;
}
}
return 0;
}
答案 0 :(得分：0)
您不应在root中明确使用树main()，并且通常不在树的方法之外。要实现这一点，只需制作方法
avl_node* insert(avl_node *where, int value)
在类中私有（或至少受保护）并添加公共接口：
void insert(int value)
{
root = insert(root, value);
}
然后在main中，只需调用
即可添加项目 avlTree tree;
....
tree.insert(item);
编辑回答评论中提出的问题。
display，inorder等函数应该像insert一样处理：声明一个公共的无参数函数来启动动作，一个带有参数的受保护方法以递归方式执行：
public:
void display() { display(root, 0); }
void inorder() { inorder(root); }
.....
protected:
void display(avl_node *node, int level)
{
if (node!=NULL)
{
display(node->right, level + 1);
if (node == root)
cout << "Root -> ";
else
cout << " ";
cout << setw(5*level) << "" << node->data << endl;
display(node->left, level + 1);
}
}
void inorder(avl_node *node)
{
if (node)
{
inorder (node->left);
cout << node->data << " ";
inorder (node->right);
}
}
然后使用：
tree.display();
tree.inorder();