python 2.6 引入了itertools模塊，使得排列組合的實(shí)現(xiàn)非常簡(jiǎn)單：
import itertools
有序排列：e.g., 4個(gè)數(shù)內(nèi)選2個(gè)排列：
>>> print list(itertools.permutations([1,2,3,4],2))
[(1, 2), (1, 3), (1, 4), (2, 1), (2, 3), (2, 4), (3, 1), (3, 2), (3, 4), (4, 1), (4, 2), (4, 3)]
無(wú)序組合：e.g.,4個(gè)數(shù)內(nèi)選2個(gè)：
>>> print list(itertools.combinations([1,2,3,4],2))
[(1, 2), (1, 3), (1, 4), (2, 3), (2, 4), (3, 4)]
