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public class MinHeap<T extends Comparable<? super T>> implements MinHeapInterface<T>
{
private T[] heap;
private int lastIndex;
private static final int DEFAULT_INITIAL_CAPACITY = 25;
public MinHeap()
{
this(DEFAULT_INITIAL_CAPACITY);
}
public MinHeap(int initialCapacity)
{
@SuppressWarnings("unchecked")
T[] tempHeap = (T[]) new Comparable[initialCapacity];
heap = tempHeap;
lastIndex = 0;
}
public void add(T newEntry)
{
lastIndex++;
ensureCapacity();
int newIndex = lastIndex;
int parentIndex = newIndex / 2;
while((parentIndex > 0) && newEntry.compareTo(heap[parentIndex]) < 0)
{
heap[newIndex] = heap[parentIndex];
newIndex = parentIndex;
parentIndex = newIndex / 2;
}
heap[newIndex] = newEntry;
}
public T removeMin()
{
T root = null;
if(!isEmpty())
{
root = heap[1];
heap[1] = heap[lastIndex];
lastIndex--;
reheap(1);
}
return root;
}
public T getMin()
{
T root = null;
if(!isEmpty())
{
root = heap[1];
}
return root;
}
public boolean isEmpty()
{
return lastIndex < 1;
}
public int getSize()
{
return lastIndex;
}
public void clear()
{
for(int i = 0; i <= lastIndex; i++)
{
heap[i] = null;
}
lastIndex = 0;
}
private void ensureCapacity()
{
if(heap.length == lastIndex)
{
@SuppressWarnings("unchecked")
T[] tempHeap = (T[]) new Comparable[heap.length * 2];
for(int i = 0; i < lastIndex; i++)
{
tempHeap[i] = heap[i];
}
heap = tempHeap;
}
}
private void reheap(int rootIndex)
{
boolean done = false;
T orphan = heap[rootIndex];
int leftChildIndex = rootIndex * 2;
while(!done && (leftChildIndex <= lastIndex))
{
int smallerChildIndex = leftChildIndex;
int rightChildIndex = leftChildIndex + 1;
if((rightChildIndex <= lastIndex) && heap[rightChildIndex].compareTo(heap[smallerChildIndex]) < 0)
{
smallerChildIndex = rightChildIndex;
}
if(orphan.compareTo(heap[smallerChildIndex]) > 0)
{
heap[rootIndex] = heap[smallerChildIndex];
rootIndex = smallerChildIndex;
leftChildIndex = rootIndex * 2;
}
else
{
done = true;
}
}
heap[rootIndex] = orphan;
}
}
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