[Leetcode] 40. 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] 

import java.util.ArrayList;public class Solution {    public ArrayList<ArrayList<Integer>> combinationSum2(int[] candidates, int target) {        ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>();        if(candidates == null || candidates.length == 0) return result;        Arrays.sort(candidates);        ArrayList<Integer> list = new ArrayList<Integer>();        helper(candidates, target, result, list, 0);        return result;    }    private void helper(int[] candidates, int target, ArrayList<ArrayList<Integer>> result, ArrayList<Integer> list, int start){        if(target < 0) return;        if(target == 0){            result.add(new ArrayList<Integer>(list));        }        for(int i = start; i < candidates.length; i++){            if(i == start || candidates[i] != candidates[i - 1]){                list.add(candidates[i]);                helper(candidates, target - candidates[i], result, list, i + 1);                list.remove(list.size() - 1);            }        }    }}