216. Combination Sum III

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class Solution {
    private void util(List<List<Integer>> res,List<Integer> ls,int k,int n,int start){
        if(ls.size()>k) return;

        if(ls.size()==k&&n==0) {
            res.add(new ArrayList<>(ls));
            return;
        }

        for(int i=start;i<=n&&i<=9;i++){
                ls.add(i);
                util(res,ls,k,n-i,i+1);
                ls.remove(ls.size()-1);
        }    
    }

    public List<List<Integer>> combinationSum3(int k, int n) {
        List<List<Integer>> res=new ArrayList<>();
        util(res,new ArrayList<Integer>(),k,n,1);
        return res;
    }
}
/*
class Solution {
    private void util(Set<List<Integer>> set,List<Integer> ls,int k,int n){
        // System.out.println(ls+","+n);
        if(ls.size()==k&&n!=0) return;
        if(ls.size()==k&&n==0) {
            ArrayList<Integer> a_ls=new ArrayList<>(ls);
            Collections.sort(a_ls);
            set.add(a_ls);
        }›
        for(int i=1;i<=9;i++){
            if(!ls.contains(i)&&ls.size()<k){
                ls.add(i);
                util(set,ls,k,n-i);
                ls.remove(ls.size()-1);
            }
        }
        
    }
    public List<List<Integer>> combinationSum3(int k, int n) {
        Set<List<Integer>> set=new HashSet<>();
        util(set,new ArrayList<Integer>(),k,n);
        List<List<Integer>> res=new ArrayList<>(set);
        return res;
    }
}
*/

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