# Combination Sum II

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]
]
```

```java
class Solution {
    public List<List<Integer>> combinationSum2(int[] nums, int target) {
        List<List<Integer>> list = new ArrayList<>();
        Arrays.sort(nums);
        backtrack(list, new ArrayList<>(), nums, target, 0);
        return list;

    }

    private void backtrack(List<List<Integer>> list, List<Integer> temp, int[] nums, int target, int start) {
        if (target <= 0) {
            if (target == 0)
                list.add(new ArrayList<>(temp));
            return;
        }
        for (int i = start; i < nums.length; i++) {
            if (i > start && nums[i] == nums[i - 1])
                continue; // skip duplicates
            temp.add(nums[i]);
            backtrack(list, temp, nums, target - nums[i], i + 1);
            temp.remove(temp.size() - 1);
        }
    }
}
```
