回溯问题

class Solution(object):
def combine(self, n, k):
def backtrack(startindex):
for i in range(startindex,n+2):
print(path)
if len(path)==k:
result.append(path[:])
return
path.append(i)
backtrack(i+1)
path.pop()
backtrack(1)
return result
基本组合问题N=2 K=4
[[1,2],[1,3],[1,4],[2,3],[2,4],[3,4]]