/// <summary>
/// Create or get an element in the vector.
/// </summary>
/// <param name="index">Index in the vector</param>
/// <returns>The vector element at the specified index</returns>
public VectorElement <T> GetElement(int index)
{
if (index < 0)
{
throw new ArgumentException("Invalid index {0}".FormatString(index));
}
if (index == 0)
{
return(_trashCan);
}
// Expand the vector if it is necessary
if (index > Length)
{
Length = index;
}
// Find the element
SparseVectorElement element = _firstInVector, lastElement = null;
while (element != null)
{
if (element.Index > index)
{
break;
}
if (element.Index == index)
{
return(element);
}
lastElement = element;
element = element.NextInVector;
}
// Create a new element
var result = new SparseVectorElement(index);
// Update links for last element
if (lastElement == null)
{
_firstInVector = result;
}
else
{
lastElement.NextInVector = result;
}
result.PreviousInVector = lastElement;
// Update links for next element
if (element == null)
{
_lastInVector = result;
}
else
{
element.PreviousInVector = result;
}
result.NextInVector = element;
return(result);
}
/// <summary>
/// Swap two elements.
/// </summary>
/// <param name="index1">The index of the first element.</param>
/// <param name="index2">The index of the second element.</param>
public void Swap(int index1, int index2)
{
if (index1 < 0 || index2 < 0)
{
throw new SparseException("Invalid indices {0} and {1}".FormatString(index1, index2));
}
if (index1 == index2)
{
return;
}
if (index2 < index1)
{
var tmp = index1;
index1 = index2;
index2 = tmp;
}
// Get the two elements
SparseVectorElement first = null, second = null;
// Find first element
var element = _firstInVector;
while (element != null)
{
if (element.Index == index1)
{
first = element;
}
if (element.Index > index1)
{
break;
}
element = element.NextInVector;
}
// Find second element
while (element != null)
{
if (element.Index == index2)
{
second = element;
}
if (element.Index > index2)
{
break;
}
element = element.NextInVector;
}
// Swap these elements
Swap(first, second, index1, index2);
}
/// <summary>
/// Remove an element.
/// </summary>
/// <param name="element">Element to be removed.</param>
private void Remove(SparseVectorElement element)
{
// Update surrounding links
if (element.PreviousInVector == null)
{
_firstInVector = element.NextInVector;
}
else
{
element.PreviousInVector.NextInVector = element.NextInVector;
}
if (element.NextInVector == null)
{
_lastInVector = element.PreviousInVector;
}
else
{
element.NextInVector.PreviousInVector = element.PreviousInVector;
}
}
/// <summary>
/// Swaps the specified elements.
/// </summary>
/// <param name="first">The first element.</param>
/// <param name="second">The second element.</param>
/// <param name="index1">The index of the first element.</param>
/// <param name="index2">The index of the second element.</param>
private void Swap(SparseVectorElement first, SparseVectorElement second, int index1, int index2)
{
// Nothing to do
if (first == null && second == null)
{
return;
}
// Swap the elements
if (first == null)
{
// Do we need to move the element?
if (second.PreviousInVector == null || second.PreviousInVector.Index < index1)
{
second.Index = index1;
return;
}
// Move the element back
var element = second.PreviousInVector;
Remove(second);
while (element.PreviousInVector != null && element.PreviousInVector.Index > index1)
{
element = element.PreviousInVector;
}
// We now have the element below the insertion point
if (element.PreviousInVector == null)
{
_firstInVector = second;
}
else
{
element.PreviousInVector.NextInVector = second;
}
second.PreviousInVector = element.PreviousInVector;
element.PreviousInVector = second;
second.NextInVector = element;
second.Index = index1;
}
else if (second == null)
{
// Do we need to move the element?
if (first.NextInVector == null || first.NextInVector.Index > index2)
{
first.Index = index2;
return;
}
// Move element forward
var element = first.NextInVector;
Remove(first);
while (element.NextInVector != null && element.NextInVector.Index < index2)
{
element = element.NextInVector;
}
// We now have the first element above the insertion point
if (element.NextInVector == null)
{
_lastInVector = first;
}
else
{
element.NextInVector.PreviousInVector = first;
}
first.NextInVector = element.NextInVector;
element.NextInVector = first;
first.PreviousInVector = element;
first.Index = index2;
}
else
{
// Are they adjacent or not?
if (first.NextInVector == second)
{
// Correct surrounding links
if (first.PreviousInVector == null)
{
_firstInVector = second;
}
else
{
first.PreviousInVector.NextInVector = second;
}
if (second.NextInVector == null)
{
_lastInVector = first;
}
else
{
second.NextInVector.PreviousInVector = first;
}
// Correct element links
first.NextInVector = second.NextInVector;
second.PreviousInVector = first.PreviousInVector;
first.PreviousInVector = second;
second.NextInVector = first;
first.Index = index2;
second.Index = index1;
}
else
{
// Swap surrounding links
if (first.PreviousInVector == null)
{
_firstInVector = second;
}
else
{
first.PreviousInVector.NextInVector = second;
}
first.NextInVector.PreviousInVector = second;
if (second.NextInVector == null)
{
_lastInVector = first;
}
else
{
second.NextInVector.PreviousInVector = first;
}
second.PreviousInVector.NextInVector = first;
// Swap element links
var element = first.PreviousInVector;
first.PreviousInVector = second.PreviousInVector;
second.PreviousInVector = element;
element = first.NextInVector;
first.NextInVector = second.NextInVector;
second.NextInVector = element;
first.Index = index2;
second.Index = index1;
}
}
}
