# 40. Combination Sum II (Medium)

https://leetcode.com/problems/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],

]
```

## Solutions

• Java
``````public class Solution {
public List<List<Integer>> combinationSum2(int[] candidates, int target) {
List<List<Integer>> rst = new ArrayList<>();
if (candidates == null) return rst;

Arrays.sort(candidates);
combine(rst, new ArrayList<Integer>(), candidates, target, 0);

return rst;
}

private void combine(List<List<Integer>> rst, List<Integer> solution, int[] nums, int target, int depth) {
if (target < 0) {
return;
}

if (target == 0) {
return;
}

for (int i = depth; i < nums.length; i++) {
if (nums[i] > target) {
break;
}

// since the nums are sorted, the following if case will be redundant
if (i > depth && nums[depth] == nums[i]) {
continue;
}

// nums[i-1] has already swapped
// swap(nums, depth, i) makes no difference
if (i > depth && nums[i] == nums[i - 1]) {
continue;
}