LeetCode--subsets（数组的所有可能子集合）

题目描述

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],
  []
]

Solution 1 

//AC版本
class Solution {
public:
    void dfs(vector<vector<int> >&res,vector<int>ans,int val,int size,vector<int> &S)
    {
        if(val>=size) return ;
        for(int i=val;i<size;++i)
        {
            ans.push_back(S[i]);
            res.push_back(ans);
            dfs(res,ans,i+1,size,S);
            ans.pop_back();
        }
        return ;
    }
    vector<vector<int> > subsets(vector<int> &S) {
        vector<vector<int> >res;
        sort(S.begin(),S.end());
        res.push_back({});
        vector<int>ans;
        dfs(res,ans,0,S.size(),S);
        for(int i=0;i<res.size()-1;++i)
            for(int j=0;j<res.size()-i;++j)
                if(res[j].size()>res[j+1].size())
                    swap(res[j],res[j+1]);
        return res;
    }
};

Solution 2

//顺序不对，不过也不失一种好办法
class Solution {
public:
    vector<int> GetSub(int x,vector<int>&S)
    {
        vector<int>temp;
        for(int i=1;i<=static_cast<int>(S.size());++i)
        {
            if(x&1) temp.push_back(S[i-1]);
            x=x>>1;
        }
        return temp;
    }
    vector<vector<int> > subsets(vector<int> &S) {
        vector<vector<int> >res;
        sort(S.begin(),S.end(),less<int>());
        int MaxSize=1<<S.size();
        for(int i=0;i<MaxSize;++i)
            res.push_back(GetSub(i,S));
        return res;
    }
};