Subsets 集合子集 回溯

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],
  []
]

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 Array Backtracking Bit Manipulation

 

递归，放与不放的问题。转化成生成树

class Solution {
private:
    vector<vector<int> > ret;
public:
    void generate(vector<int> vet,vector<int> &S,int i){
        if(i==S.size()){
            ret.push_back(vet);
            return;
        }
        generate(vet,S,i+1);        //相当于取右子树
        vet.push_back(S[i]);             
        generate(vet,S,i+1);       //相当于取左子树
    }
    vector<vector<int> > subsets(vector<int> &S) {
        ret.clear();
        sort(S.begin(),S.end());
        vector<int> vet;
        generate(vet,S,0);
        return ret;
    }
};