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## Problem

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

Each number in candidates 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. Example 1:

Input: candidates = [10,1,2,7,6,1,5], target = 8,
A solution set is:
[
[1, 7],
[1, 2, 5],
[2, 6],
[1, 1, 6]
]


Example 2:

Input: candidates = [2,5,2,1,2], target = 5,
A solution set is:
[
[1,2,2],
[5]
]


Constraints:

• 1 <= candidates.length <= 100
• 1 <= candidates[i] <= 50
• 1 <= target <= 30

## Code

class Solution {
public List<List<Integer>> combinationSum2(int[] candidates, int target) {
List<List<Integer>> res = new ArrayList<>();
Arrays.sort(candidates);
helper(res, candidates, target, new ArrayList<>(), 0);
return res;
}

private void helper(List<List<Integer>> res,
int[] nums,
int target,
List<Integer> temp,
int start){
if(target < 0) return;
if(target == 0){
return;
}

for(int i = start; i < nums.length; i++){
// 重复的数字不能再使用了
if(i != start && nums[i] == nums[i - 1]) continue;