Am 15.07.2014 02:10 schrieb LJ:
Hi All.
I'm coding a Dynamic Programming algorithm to solve a network flow problem. At
some point in the algorithm I have to iterate through a set of nodes, while
adding and/or removing elements, until the set is empty. I know a regular set()
object does not work in a case like this, so I wonder if anyone knows of an
efficient pythonic way to handle this.
Thanks in advance!
This sounds like you want to avoid processing of an item as soon as it
is removed.
Then I'd suggest the following:
add = set()
remove = set()
while myset or add:
for item in myset:
if item not in remove:
# process
myset -= remove
myset += add
remove.clear()
add.clear()
Adding happens via add.add(item), removing via remove.add(item).
If there is additionally the need to take care in which order to apply
add/remove, or if it can happen that item X is added and removed in the
same loop run, it gets a bit more complicated.
Then adding would be like
if item in remove:
remove.remove(item)
elif item not in myset and item not in add:
add.add(item)
and removing like
if item in add:
add.remove(item)
elif item in myset:
remove.add(item)
HTH,
Thomas
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