Subset Generation I

Description
Generate all the subsets of {A, B, …, } of n elements. There are 2n subsets in total. You should guarantee that the output follows the lexicographical order.

Input
An integer n (n<=9).

Output
Output all the subsets of {A, B, …, } of n elements. In each subset, the elements should be printed from smallest to largest.

Sample Input
3

Sample Output

A
AB
ABC
AC
B
BC
C

Hint
The first line in the sample output is a blank line, which corresponds to an empty set.

Yizuodi的答案（未递归实现）

#include <iostream>
#include <sstream>
#include <set>
using namespace std;
int main()
{
    int num;
    cin>>num;
    string s[num];
    int subsetnum=1;
    for (int i = 0; i < num; i++)
    {
        s[i]='A'+i;
        subsetnum*=2;
    }
    multiset<string> sset;
    for (int i = 0; i < subsetnum; i++)
    {
        stringstream ss;
        int binarydata = i;
        int j = 0;
        while(binarydata)
        {
            if (binarydata & 1)
            {
                ss<<s[j];
            }
            binarydata >>= 1;
            j++;
        }
        string tmp;
        ss>>tmp;
        sset.insert(tmp);
    }
    for(multiset<string>::iterator it=sset.begin();it!=sset.end();++it){
        cout<<(*it)<<endl;
    }
}