Function ListviewBinarySearch
|
| Parameters :
| listview: listview to search, assumed to be sorted, must
| be <> nil.
| Item : item caption to search for, cannot be empty
| index : returns the index of the found item, or the
| index where the item should be inserted if it is not
| already in the list.
| Returns : True if there is an item with the passed caption
| in the list, false otherwise.
| Description:
| Uses a binary search and assumes that the listview is sorted
| ascending on the caption of the listitems. The search is
| case-sensitive, like the default alpha-sort routine used by
| the TListview class.
| Note:
| We use the lstrcmp function for string comparison since it
| is the function used by the default alpha sort routine. If
| the listview is sorted by another means (e.g. OnCompare event)
| this needs to be changed, the comparison method used must
| always be the same one used to sort the listview, or the
| search will not work!
| Error Conditions: none
|
Code: |
|
{+------------------------------------------------------------ | Function ListviewBinarySearch | +------------------------------------------------------------}
function ListviewBinarySearch(listview: TListview; const Item: string; var Index: Integer): Boolean; var First, last, pivot, res: Integer; begin Assert(Assigned(listview)); Assert(Length(item) > 0);
Result := False; Index := 0; if listview.Items.Count = 0 then Exit;
First := 0; last := listview.Items.Count - 1; repeat pivot := (First + last) div 2; res := lstrcmp(PChar(item), PChar(listview.Items[pivot].Caption)); if res = 0 then begin { Found the item, return its index and exit. } Index := pivot; Result := True; Break; end { If } else if res > 0 then begin { Item is larger than item at pivot } First := pivot + 1; end { If } else begin { Item is smaller than item at pivot } last := pivot - 1; end; until last < First; Index := First; end; { ListviewBinarySearch } |
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