Subsets

Given a set of distinct integers, 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 = [1,2,3], a solution is:

[
  [3],
  [1],
  [2],
  [1,2,3],
  [1,3],
  [2,3],
  [1,2],
  []
]
void visit(vector<int> &S, int n, int target, int count, int pos, vector<int> &a, vector<vector<int> > &result)
{
	if (count == target)
	{
		result.push_back(a);
		return;
	}
	
	if (pos == n)
	{
		return;
	}
	
	a.push_back(S[pos]);
	visit(S, n, target, count+1, pos+1, a, result);
	a.pop_back();
	visit(S, n, target, count, pos+1, a, result);
}

vector<vector<int> > subsets(vector<int> &S) 
{
	int n = S.size();
	vector<vector<int> > result;
	vector<int> a;
	result.push_back(a);
	for (int i = 1; i <= n; i++)
	{
		visit(S, n, i, 0, 0, a, result);
	}
	
	return result;
}