leetcode： Combination Sum

写得比较复杂，深搜吧 也没有什么很好地办法。

public class Solution {

    public ArrayList<ArrayList<Integer>> combinationSum(int[] candidates, int target) {
Arrays.sort(candidates);
return DFS(candidates,target,0,candidates.length);

    }

public static ArrayList<ArrayList<Integer>> DFS(int[] candidates, int target,int begin,int end) {

        ArrayList<ArrayList<Integer>> rst=new ArrayList<ArrayList<Integer>>();

        ArrayList<Integer> rst_ent=new ArrayList<Integer>();

        ArrayList<Integer> rst_empty=new ArrayList<Integer>();
int n=end-begin;
int i,j;
if(n==0)
return null;
if(n==1 && candidates[begin]==target)
{
rst_ent.add(candidates[begin]);
rst.add(rst_ent);
return rst;
}
i=0;
int tmp;
int last;
ArrayList<ArrayList<Integer>> subrst;
while(i*candidates[begin]<=target)
{

tmp=target-i*candidates[begin];

//if(i== 0&& begin ==2)
//System.out.println(candidates[begin]+" "+candidates[end-1]+" "+target+" ");
rst_ent=new ArrayList<Integer>();
for(j=0;j<i;j++)
rst_ent.add(candidates[begin]);
if(tmp==0)
{
rst.add(rst_ent);
break;
}
subrst=DFS(candidates, tmp,begin+1,end);

if(subrst==null)
{
i++;
continue;
}
for(j=0;j<subrst.size();j++)
{
rst_empty=new ArrayList<Integer>();
rst.add(rst_empty);
last=rst.size()-1;
rst.get(last).addAll(rst_ent);
rst.get(last).addAll(subrst.get(j));
}
i++;

}

        return rst;

    }

}