#include
#include
using namespace std;
void solution(int i,vector &nums,vector &item,vector > &result)   //傳引用 
{
    if(i >= nums.size())
    return ;

    item.push_back(nums[i]);
    result.push_back(item);
    solution(i+1,nums,item,result);

    item.pop_back();
    solution(i+1,nums,item,result);
}
int main()
{
    vector nums;
    nums.push_back(1);
    nums.push_back(2);
    nums.push_back(3);
    vector item;
    vector >result;
    int i = 0;
    result.push_back(item);    //將空集push進result 
    solution(i,nums,item,result);
    for(int i = 0; i < (1<< nums.size()); i++)
    {
        if(result[i].size() == 0)
        {
            cout<<"[]";
        }
        for(int j = 0; j < result[i].size(); j++)
        {
            cout<<"["<