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public class FrequencyBag<T>
{
// TO DO: Instance Variables
private FNode head;
private boolean hasChanged = true;
private int max;
//Tracks the number of times add has been called
private int total;
/**
* Constructor
* Constructs an empty frequency bag.
*/
public FrequencyBag()
{
head = null;
}
/**
* Adds new entry into this frequency bag.
* @param aData the data to be added into this frequency bag.
*/
public void add(T aData)
{
//Add to the start to make add an O(1) operation
if(!addhelper(head,aData))
{
hasChanged = true;
FNode n = new FNode(aData,head);
head = n;
}
total++;
}
public boolean addhelper(FNode head, T data)
{
if(head == null)
{
//We haven't found the item in the list, return false
return false;
}
if(head.getObject().equals(data))
{
head.add();
return true;
}
return addhelper(head.getNext(),data);
}
/**
* Gets the number of occurrences of aData in this frequency bag.
* @param aData the data to be checked for its number of occurrences.
* @return the number of occurrences of aData in this frequency bag.
*/
public int getFrequencyOf(T aData)
{
return getFrequencyOfHelper(head,aData);
}
public int getFrequencyOfHelper(FNode<T> node,T data)
{
//If we've hit a null node, the object isn't in the list
if(node == null)
{
return 0;
}
if(node.getObject().equals(data))
{
return node.getFrequency();
}
else
{
return getFrequencyOfHelper(node.getNext(),data);
}
}
/**
* Gets the maximum number of occurrences in this frequency bag.
* @return the maximum number of occurrences of an entry in this
* frequency bag.
*/
public int getMaxFrequency()
{
if(hasChanged)
{
hasChanged = false;
max = getMaxFrequencyHelper(head);
return max;
}
else
{
return max;
}
}
private int getMaxFrequencyHelper(FNode<T> node)
{
if(node == null) //Were at the end
return 0;
int nmax = getMaxFrequencyHelper(node.getNext());
return node.getFrequency() > nmax?node.getFrequency():nmax;
}
/**
* Gets the probability of aData
* @param aData the specific data to get its probability.
* @return the probability of aData
*/
public double getProbabilityOf(T aData)
{
return getFrequencyOf(aData)/(total*1.0);
}
/**
* Empty this bag.
*/
public void clear()
{
head = null;
hasChanged = true;
total = 0;
}
/**
* Gets the number of entries in this bag.
* @return the number of entries in this bag.
*/
public int size()
{
return total;
}
public class FNode<T>
{
private T object = null;
private int frequency = 1;
private FNode next = null;
public FNode()
{
}
public FNode(T obj,FNode n)
{
object = obj;
next = n;
}
public void setObject(T obj)
{
object = obj;
}
public T getObject()
{
return object;
}
public void add()
{
frequency++;
}
public int getFrequency()
{
return frequency;
}
public FNode getNext()
{
return next;
}
public void setNext(FNode n)
{
next = n;
}
}
}
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