Combination Sum II

Given a collection of candidate numbers (C) and a target number (T), find all unique combinations in C where the candidate numbers sums to T.

Each number in C may only be used once in the combination.

Note:

• All numbers (including target) will be positive integers.
• Elements in a combination (a1, a2, … , ak) must be in non-descending order. (ie, a1 ≤ a2 ≤ … ≤ ak).
• The solution set must not contain duplicate combinations.

For example, given candidate set 10,1,2,7,6,1,5 and target 8, 
A solution set is: 
[1, 7] 
[1, 2, 5] 
[2, 6] 
[1, 1, 6] 

public class Solution {    public List<List<Integer>> combinationSum2(int[] num, int target) {        LinkedList<List<Integer>> res=new LinkedList<List<Integer>>();        LinkedList<Integer> list=new LinkedList<Integer>();        if(num==null || num.length<=0) return res;        Arrays.sort(num);        dfs(0,0,target,num,list,res);        HashSet set=new HashSet(res);        res.clear();        res.addAll(set);        return res;    }    public void dfs(int start,int sum,int target,int[] num,LinkedList<Integer> list,List<List<Integer>> res){        if(sum==target){            LinkedList<Integer> l=new LinkedList<Integer>(list);            res.add(l);            return;        }        for(int i=start;i<num.length;i++){            if(sum+num[i]>target) return;            list.add(num[i]);            dfs(i+1,sum+num[i],target,num,list,res);            list.pollLast();        }    }}