标签：content inpu 组合 self out div import find elf
itertools mode 中 combinations的功能：
from itertools import combinations
print list(combinations(list,r))
将打印 list中的所有长度为r的，子集的合集
e.g.
from itertools import combinations
list = [1,2,3]
print (list(combinations(list,2)))
>>>
[(1,2),(1,3),(2,3)]
所以当遇到排列组合的问题时，combinations会很好用
leetcode例题：
216. Combination Sum III
Find all possible combinations of k numbers that add up to a number n, given that only numbers from 1 to 9 can be used and each combination should be a unique set of numbers.
Note:
Example 1:
Input: k = 3, n = 7 Output: [[1,2,4]]
Example 2:
Input: k = 3, n = 9 Output: [[1,2,6], [1,3,5], [2,3,4]]
思路：利用combinations列出符合长度k的子集，再筛选出合为n的子集
from itertools import combinations
class Solution(object):
def combinationSum3(self, k, n):
return [res for res in combinations(range(1,10),k) if sum(res) == n]
详细点的写法：
from itertools import combinations
class Solution(object):
def combinationSum3(self, k, n):
res = []
raw = combinations(range(1,10),k)
for i in raw:
if sum(i) == n:
res.append(i)
return res
itertools mode 之 combinations用法
标签：content inpu 组合 self out div import find elf
原文地址：https://www.cnblogs.com/phinza/p/10231257.html
