def _assure_length(self, l):
if l in self.permutations:
return
if l == 0:
self.permutations[0] = []
maybe = Permutation([])
if maybe.avoids(*self.avoidance):
self.permutations[0].append(maybe)
else:
self._assure_length(l-1)
here = set()
for p in self.permutations[l-1]:
for i in range(l):
q = Permutation(p[:i] + (l,) + p[i:])
if q.avoids(*self.avoidance):
here.add(q)
self.permutations[l] = list(here)
def _assure_length(self, l):
if l in self.permutations:
return
if l == 0:
self.permutations[0] = []
maybe = Permutation([])
if maybe.avoids(*self.avoidance):
self.permutations[0].append(maybe)
else:
self._assure_length(l - 1)
here = set()
for p in self.permutations[l - 1]:
for i in range(l):
q = Permutation(p[:i] + (l, ) + p[i:])
if q.avoids(*self.avoidance):
here.add(q)
self.permutations[l] = here
