40. 组合总和 II-LeetCode

 1 class Solution {
 2       public List<List<Integer>> combinationSum2(int[] candidates, int target){
 3            LinkedList<List<Integer>> list=new LinkedList<>();
 4             if(candidates==null||candidates.length==0)
 5                 return list;
 6             Arrays.sort(candidates);
 7             rec(0,list,new LinkedList<Integer>(),candidates,target);
 8             return list;
 9         }
10     public void rec(int index,LinkedList<List<Integer>> list,LinkedList<Integer> tmp,int[] candidates,int target)
11        {
12          if(target<0)
13              return;
14          else if(target==0)
15          {        
16              list.add(new LinkedList(tmp));
17              return;
18          }
19          else
20          {
21              for(int i=index;i< candidates.length&&candidates[i]<=target;i++)//这个剪枝条件就可以提高
                                                                                //速度
22              {
23                  if(i!=index&&candidates[i]==candidates[i-1])
24                      continue;
25                  tmp.add(candidates[i]);
26                  rec(i+1,list,tmp,candidates,target-candidates[i]);
27                  tmp.removeLast();
28              }
29          }
30        }
31 }