def complement(p, c):
results = PostingsList()
while p is not None:
# c cannot overtake p as c is everything,
# and both move together when equal
if p.entry == c.entry:
p = next_or_none(p)
c = next_or_none(c)
else:
results.add(c.entry)
c = next_or_none(c)
if c is not None:
add_until_end(c, results)
return results
def intersect(p1, p2):
if p1 is None or p2 is None:
return None
results = PostingsList()
while p1 is not None and p2 is not None:
if p1.entry == p2.entry:
results.add(p1.entry)
p1 = next_or_none(p1)
p2 = next_or_none(p2)
elif p1.entry < p2.entry:
p1 = next_or_skip(p1, p2.entry)
else:
p2 = next_or_skip(p2, p1.entry)
return results
def union(p1, p2):
if p1 is None and p2 is None:
return None
results = PostingsList()
while p1 is not None or p2 is not None:
if p1 is None:
add_until_end(p2, results)
p2 = None
elif p2 is None:
add_until_end(p1, results)
p1 = None
else:
if p1.entry < p2.entry:
results.add(p1.entry)
p1 = next_or_none(p1)
elif p1.entry == p2.entry:
results.add(p1.entry)
p1 = next_or_none(p1)
p2 = next_or_none(p2)
else:
results.add(p2.entry)
p2 = next_or_none(p2)
return results