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.

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]]

public class Solution {
public List<List<Integer>> combinationSum3(int k, int n) {
List<List<Integer>> list=new ArrayList<>();
combination(list,new ArrayList<Integer>(),k,n,1);
return list;
}
public void combination(List<List<Integer>> list,List<Integer> comb,int k,int n,int start){
if(comb.size()==k&&n==0){
list.add(new ArrayList<>(comb));
return;
}
for(int i=start;i<10;i++){
comb.add(i);
combination(list,comb,k,n-i,i+1);
comb.remove(comb.size()-1);
}
}
}