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.
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]]
class Solution(object):
def combinationSum3(self, k, n):
"""
:type k: int
:type n: int
:rtype: List[List[int]]
"""
ans = []
path = []
if k<=0 or n<=0:
return ans
self.comb_helper(k, n, 1, path, ans)
return ans
def comb_helper(self, k, n, start, path, ans):
if n<0:
return
if n==0 and k==0:
ans.append(list(path))
return
for i in xrange(start, 10):
path.append(i)
self.comb_helper(k-1, n-i, i+1, path, ans)
path.pop()
