leetcode : 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.
• 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[] candidates, int target) {
        List<List<Integer>> result = new ArrayList<List<Integer>>();
        if(candidates == null || candidates.length == 0) {
            return result;
        }
        List<Integer> list = new ArrayList<Integer>();
        Arrays.sort(candidates);
        helper(result, list, candidates, 0, target);
        return result;
    }
    
    public void helper(List<List<Integer>> result, List<Integer> list, int[] nums, int position, int remain) {
        if(remain < 0) {
            return;
        }
        if(remain == 0) {
            result.add(new ArrayList<Integer>(list));
        }
        for(int i = position; i < nums.length; i++) {
            if(i > position && nums[i] == nums[i - 1]) {
                continue;
            }
            list.add(nums[i]);
            helper(result, list, nums, i + 1, remain - nums[i]);
            list.remove(list.size() - 1);
        }
    }
}