// Delete the mininum node, and return it. This is where the log n
// magic happens. Pairs the sub-list together, then sweeps up the pairs
// into one tree again.
public T deleteMin()
{
if (isEmpty())
{
return(default(T));
}
// NOTE: the final_cast is needed so the user can modify his own data.
T ret = top.getNode();
HeapNode <T> newtop, i, j;
if (top.getChild() == null) // Only one element in heap
{
top = null;
size--;
return(ret);
}
// First of two passes: combine pairs of roots together, from
// left to right.
i = top.getChild();
// Note, end condition is too complicated for more generalized loops
while (true)
{ // i is the first, j is the second
if ((j = i.getNext()) == null) // If i is the odd man out (no partner j)
{
break;
}
if (i == merge(i, j)) // i came out on top
{
if (i.getNext() == null) // i is now the last in the loop
{
break;
}
i = i.getNext();
}
else // j came out on top
{
if (j.getNext() == null) // j is the last in the loop
{
i = j; // As a set up for the next pass
break;
}
i = j.getNext();
}
}
// Iterate the other way, combining each new tree with the rightmost
newtop = i;
j = i.getPrev();
while (j != null)
{
newtop = merge(newtop, j);
j = newtop.getPrev();
}
top = newtop;
size--;
return(ret);
}