leetcode 216 组合总和3

避免顺序不同，同时控制长度与和

class Solution:
    def combinationSum3(self, k: int, n: int) -> List[List[int]]:
        def dfs(i,path,target,n,k,result):
            if target==n and len(path)==k:
                result.append(path[:])
                return 
            elif target==n and len(path)!=k:
                return 

            elif len(path)>=k:
                return 

            for j in range(i,10):
                path.append(j)
                dfs(j+1,path,target+j,n,k,result)
                path.pop()
        result=[]
        dfs(1,[],0,n,k,result)
        return result