C++ linked hashtable copying - c++

Question

I have to implement a HashTable with linked lists. It is almost done (still missing templates, will do in time), but I'm stuck at something.
Basically, I want to resize my hashtable when the load factor reaches a given value, say 50%. But I don't know how I should do it.
I have a basic idea:
Create a temporary HT with the new size
Hash every data in every list from the old HT to the temporary one
Delete the old HT
Return the temporary HT
I can't figure out an implementation for it though...
Here is what I have so far:
//List:
struct Node
{
string data;
Node *next;
};
class List
{
private:
Node *head, *tail;
int length;
friend class HashTable;
public:
List();
List(const List &L);
//~List() {delete this;};
List& operator =(List L);
int find(string);
void insert(string value);
void remove_head();
void remove_poz(int);
void remove_tail();
void clear();
void display();
};
List::List()
{
head = NULL;
tail = NULL;
length = 0;
}
List::List(const List& L)
{
Node** temp = &head;
const Node* source = L.head;
while(source)
{
*temp = new Node(*source);
temp = &(*temp)->next;
source = source->next;
}
}
List& List::operator =(List L)
{
swap(head, L.head);
return *this;
}
void List::insert(string value)
{
Node* temp = new Node;
temp->data = value;
temp->next = NULL;
if (!head)
head = temp;
if (tail)
tail->next = temp;
tail = temp;
length++;
}
void List::display()
{
Node *temp = new Node;
temp = head;
while (temp != NULL)
{
cout<<temp->data<<" ";
temp = temp->next;
}
delete temp;
}
//HashTable:
class HashTable
{
private:
List *table;
float load, stored;
int slots;
friend class List;
public:
HashTable();
HashTable(int);
~HashTable();
int hashFunc(string key);
int findTable(string);
int findList(string);
HashTable& operator =(const HashTable&);
void resize(); //I need this one
void insert(string);
void remove(string);
void clear(int);
void clear();
void display();
};
HashTable::HashTable()
{
stored = 0;
load = 0.00;
slots = 15;
table = new List[slots];
}
HashTable::HashTable(int size)
{
stored = 0;
load = 0.00;
slots = size;
table = new List[slots];
}
int HashTable::hashFunc(string key)
{
unsigned int i, ind = 0;
for (i = 0; i<key.length(); ++i)
ind = ind + key[i];
ind %= slots;
return ind;
}
HashTable& HashTable::operator =(const HashTable& T) //I suppose it is incorrect
{
int i;
HashTable temp(T.slots);
for (i = 0; i < slots; ++i)
{
temp.table[i] = T.table[i];
}
return temp;
}
void HashTable::insert(string value)
{
int ind = hashFunc(value);
table[ind].insert(value);
if (!table[ind].head->next) stored++;
load = stored / slots;
if (load > 0.50) resize();
}
(Note: only the functions that might be needed are shown here)
Any help, correction or suggestion would be much appreciated :)
UPDATE:
Managed to pull this one off:
void HashTable::resize()
{
int i;
int newSize = slots * 2;
int newLoad = stored / newSize;
HashTable HT(newSize);
Node* temp;
for (i = 0; i < slots; ++i)
{
temp = table[i].head;
while (temp != NULL)
{
HT.insert(temp->data);
temp = temp->next;
}
}
}
Now I have a new HashTable named HT, with double the size of the original one, and all elements have been inserted correctly.
But I don`t know how to proceed.

Answer 1

The easiest way to proceed is to add a swapContents() method to your HashTable class:
void HashTable::swapContents(HashTable & rhs)
{
std::swap(table, rhs.table);
std::swap(load, rhs.load);
std::swap(stored, rhs.stored);
std::swap(slots, rhs.slots);
// any other member-variables of the HashTable class would get swapped here too
}
... then call swapContents(HT) at the end of your resize() method, so that HT becomes the older/smaller HashTable (and gets discarded) while this becomes the newer/larger table.