78. Subsets

题目

 Given a set of distinct integers, nums, return all possible subsets (the power set).

Note: The solution set must not contain duplicate subsets.

For example,
If nums = [1,2,3], a solution is:

[
  [3],
  [1],
  [2],
  [1,2,3],
  [1,3],
  [2,3],
  [1,2],
  []
]

解析

// 78. Subsets
class Solution_78 {
public:
	void help(vector<vector<int>>& vecs, vector<int> &vec,vector<int> &src,int index,int k)
	{
		if (index>src.size())
		{
			return;
		}
		if (k==0)
		{
			vecs.push_back(vec);
			return;
		}

		vec.push_back(src[index]);
		help(vecs, vec, src, index + 1, k - 1);
		vec.pop_back();
		help(vecs, vec, src, index + 1, k);

		return;
	}

	vector<vector<int>> subsets(vector<int>& nums) {

		vector<vector<int>> vecs;
		vector<int> vec;

		sort(nums.begin(), nums.end());
		for (int i = 0; i <= nums.size();i++)
		{
			help(vecs, vec, nums, 0, i);
		}
		
		return vecs;
	}

     //链接：https://www.nowcoder.com/questionTerminal/c333d551eb6243e0b4d92e37a06fbfc9
	void backtracking(vector<vector<int>> &result, vector<int> &path, vector<int> &S, int n) {
		result.push_back(path);
		for (int i = n; i < S.size(); ++i) {
			path.push_back(S[i]);
			backtracking(result, path, S, i + 1);
			path.pop_back();
		}
	}
	vector<vector<int> > subsets(vector<int> &S) {
		vector<vector<int>> result;
		vector<int> path;
		if (S.size() == 0) 
			return result;
		sort(S.begin(), S.end());
		backtracking(result, path, S, 0);

		return result;
	}
};

题目来源

78. Subsets