LeetCode-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],
  []
]

注意空集

class Solution {
public:
    void Sub(vector<vector<vector<int> > >&total,vector<int>& a,int i){
        if(total[i].size()!=0){
            return;
        }
        else{
            if(i==0){
                vector<int> one;
                one.push_back(a[0]);
                total[0].push_back(one);
                total[0].push_back(vector<int>());
                return;
            }
            else{
                Sub(total,a,i-1);
                vector<vector<int> >r1=total[i-1];
                for(int j=0;j<r1.size();j++){
                    total[i].push_back(r1[j]);
                     r1[j].push_back(a[i]);
                    total[i].push_back(r1[j]);
                }
                return;
            }
        }
    }
    vector<vector<int> > subsets(vector<int> &S) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if(S.size()==0)return vector<vector<int> >();
        sort(S.begin(),S.end());
        vector<vector<vector<int> > > total(S.size());
        Sub(total,S,S.size()-1);
        vector<vector<int> >& ret=total[S.size()-1];
        set<vector<int> > res;
        for(int i=0;i<ret.size();i++)res.insert(ret[i]);
        ret=vector<vector<int> >(res.begin(),res.end());
        return ret;
    }
};