Combination Sum leetcode java

 1     public ArrayList<ArrayList<Integer>> combinationSum(int[] candidates, int target) {  
 2         ArrayList<ArrayList<Integer>> res = new ArrayList<ArrayList<Integer>>();  
 3         ArrayList<Integer> item = new ArrayList<Integer>();
 4         if(candidates == null || candidates.length==0)  
 5             return res; 
 6             
 7         Arrays.sort(candidates);  
 8         helper(candidates,target, 0, item ,res);  
 9         return res;  
10     }  
11     
12     private void helper(int[] candidates, int target, int start, ArrayList<Integer> item,   
13     ArrayList<ArrayList<Integer>> res){  
14         if(target<0)  
15             return;  
16         if(target==0){  
17             res.add(new ArrayList<Integer>(item));  
18             return;  
19         }
20         
21         for(int i=start;i<candidates.length;i++){  
22             if(i>0 && candidates[i] == candidates[i-1])//deal with dupicate
23                 continue;  
24             item.add(candidates[i]);
25             int newtarget = target - candidates[i];
26             helper(candidates,newtarget,i,item,res);//之所以不传i+1的原因是：
27                                                     //The same repeated number may be 
28                                                     //chosen from C unlimited number of times.
29             item.remove(item.size()-1);  
30         }  
31     }