LeetCode Subsets II

题目：

Given a collection of integers that might contain duplicates, S, return all possible subsets.

Note:

• Elements in a subset must be in non-descending order.
• The solution set must not contain duplicate subsets.

For example,
If S = [1,2,2], a solution is:

[
  [2],
  [1],
  [1,2,2],
  [2,2],
  [1,2],
  []
]

class Solution {
public:
	vector<vector<int> > subsetsWithDup(vector<int> &S) {
		sort(S.begin(), S.end());
		int n = S.size();
		vector<int> row;
		ans.clear();
		K.clear();
		dfs(0, row, n, S);
		ans.insert(ans.begin(), K.begin(), K.end());
		return ans;
	}
private:
	vector<vector<int>> ans;
	set<vector<int>> K;
	void dfs(int depth, vector<int> row, int n, vector<int> &S) {
		if (depth == n) {
			K.insert(row);
			return;
		}
		dfs(depth + 1, row, n, S);
		row.push_back(S[depth]);
		dfs(depth + 1, row, n, S);
	}
};