Remove an element from the middle of an std::heap

Question

I\'m using a priority queue as a scheduler with one extra requirement. I need to be able to cancel scheduled items. This equates to removing an item from the middle of the pri

Answer 1

Here's a bit of delphi code i used to remove items from a heap. I don't know this C++ of which you speak and don't have a repair function, but hey..

first the pop, so you get an idea of how the thing works:

function THeap.Pop: HeapItem;
begin
  if fNextIndex > 1 then begin
    Dec(fNextIndex);
    Result:= fBuckets[1];   //no zero element
    fBuckets[1] := fBuckets[fNextIndex];
    fBuckets[fNextIndex] := nil;
    FixHeapDown;            //this has a param defaulting to 
    end
  else
    Result:= nil;
end;

now to contrast, the deletion:

procedure THeap.Delete(Item: HeapItem);
var
  i:integer;
begin
  for i:=1 to pred(fNextIndex) do
    if Item=fBuckets[i] then begin
      dec(fNextIndex);
      fBuckets[i] := fBuckets[fNextIndex];
      fBuckets[fNextIndex] := nil;
      FixHeapDown(i);
      break;
      end;
end;

its of course a no-no to even think about doing what we're doing here, but hey, costs do change sometimes and jobs do get canceled.

enjoy. i hope this helps.