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