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Avoid O(n^2) duplication handling when building hints

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Use a set to filter out seen items to avoid doing O(n^2)
de-duplication.  For very large hints, this can take considerable
time.

Using "seen_items" to build the actual hints on the (unverified)
assumption that Python can do something "smart" to turn a set into a
frozenset faster than it can with a list.

Signed-off-by: Niels Thykier <niels@thykier.net>
This commit is contained in:
Niels Thykier 2015-05-31 22:26:16 +02:00
parent 72eb6af711
commit 843952d627
1 changed files with 11 additions and 5 deletions
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14
britney.py
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@ -2865,20 +2865,26 @@ class Britney(object):
items = [(e, excuse.ver[1])] items = [(e, excuse.ver[1])]
orig_size = 1 orig_size = 1
looped = False looped = False
seen_items = set()
seen_items.update(items)
for item, ver in items: for item, ver in items:
# excuses which depend on "item" or are depended on by it # excuses which depend on "item" or are depended on by it
items.extend( (x, excuses[x].ver[1]) for x in excuses if \ new_items = [(x, excuses[x].ver[1]) for x in excuses if \
(item in excuses[x].deps or x in excuses[item].deps) \ (item in excuses[x].deps or x in excuses[item].deps) \
and (x, excuses[x].ver[1]) not in items ) and (x, excuses[x].ver[1]) not in seen_items]
items.extend(new_items)
seen_items.update(new_items)
if not looped and len(items) > 1: if not looped and len(items) > 1:
orig_size = len(items) orig_size = len(items)
h = frozenset(items) h = frozenset(seen_items)
if h not in seen_hints: if h not in seen_hints:
mincands.append(h) mincands.append(h)
seen_hints.add(h) seen_hints.add(h)
looped = True looped = True
if len(items) != orig_size: if len(items) != orig_size:
h = frozenset(items) h = frozenset(seen_items)
if h != mincands[-1] and h not in seen_hints: if h != mincands[-1] and h not in seen_hints:
candidates.append(h) candidates.append(h)
seen_hints.add(h) seen_hints.add(h)