Content #
def permutations(S):
if not S:
return [[]]
else:
res, perms = [], permutations(S[1:])
for i, _ in enumerate(S):
for perm in perms:
res.append(perm[:i] + [S[0]] + perm[i:])
return res
将S[0]插入S[1:]的排列集合元素的每个位置。