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:

All numbers will be positive integers.
The solution set must not contain duplicate combinations.
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 List<List<Integer>> combinationSum3(int k, int n) {
       List<List<Integer>> subset = new ArrayList();
       dfs(subset,1,new ArrayList(),k,n);
       return subset;
    }  
    
    void dfs(List<List<Integer>> subset , int index ,List<Integer> current,int k,int target){
        
        if(current.size()==k){
            if(target==0){
              subset.add(new ArrayList(current));
            }
            return;
        }
        
        
        
        for(int i = index;i<=9;i++){//1------9
            current.add(i);
            dfs(subset,i+1,current,k,target-i);
            current.remove(current.size()-1);
        }      
    }
}