/// <summary>
/// Add if the input T is not present in the minheap map
/// and if the input T is present then change the priority according the the
/// priority of the input
/// </summary>
/// <param name="val"></param>
public void AddOrChangePriority(T val)
{
if (!AllEntitiesIndex.ContainsKey(val.Id))
{
Insert(val);
}
else
{
ChangePriority(val, val.Id);
}
}
/// <summary>
/// this would get the min value and delete the value from the heap.
///
/// The running time for this operation is O(logn)
/// </summary>
/// <returns></returns>
public T ExtractMin()
{
if (_currentNumberOfElements == 0)
{
throw new Exception("The heap is empty");
}
T retVal = _arrayToStoreTree[0];
Swap(0, _currentNumberOfElements - 1);
_arrayToStoreTree[_currentNumberOfElements - 1] = default(T);
AllEntities.Remove(retVal.Id);
AllEntitiesIndex.Remove(retVal.Id);
_currentNumberOfElements--;
MinHeapify(0);
return(retVal);
}
/// <summary>
/// This is basically used to change the value of the array at index and
/// rebalance the tree to follow the min heap property
///
/// We will first check whether we are increasing the priority or decreasing it,
/// If we are increasing the priority, we should percolate downwards
/// if we are decreasing the priority, we should percolate upwards
///
/// The running time needed for this operation is O(log(n))
/// </summary>
/// <param name="newVal"></param>
/// <param name="index"></param>
public void ChangePriority(T newVal, int Id)
{
if (!AllEntitiesIndex.ContainsKey(Id))
{
throw new Exception("Illegal operation");
}
int index = AllEntitiesIndex[Id];
if (_arrayToStoreTree[index].CompareTo(newVal) > 0)
{
// We have decreased the priority
// We need to percolate upwards
ChangeValueAtIndex(index, newVal);
while (index > 0)
{
int parentIndex = (int)Math.Floor((index - 1) / 2.0);
if (parentIndex >= 0 && _arrayToStoreTree[parentIndex].CompareTo(_arrayToStoreTree[index]) > 0)
{
// We need to swap the element at index with its parent
Swap(index, parentIndex);
index = parentIndex;
}
else
{
// The new added value is still greater than its parent, hence break
break;
}
}
}
else
{
//We have increased the priority
// we need to percolate the changes downwards
ChangeValueAtIndex(index, newVal);
MinHeapify(index);
}
}
