找出字符串的组合

#include<iostream>  
#include<vector>  
using namespace std;  
  
//位操作算法  
void main()  
{  
    char* data="abcd";  
    int length=strlen(data);  
    int last=(1<<length)-1;  
    cout<<last<<endl;  
      
    int i;  
    for(i=1;i<=last;i++)  
    {  
        int currentIndex=length-1;  
        while(currentIndex>=0)  
        {  
            if(i&(1<<currentIndex))  
            {  
                cout<<data[length-currentIndex-1];                  
            }  
            --currentIndex;  
        }  
        cout<<endl;  
    }  
}  

void algorithm(char* data,int num,vector<char>& result)  
{  
    if(!num)  
    {  
        vector<char>::iterator it=result.begin();  
        for(it;it!=result.end();++it)  
        {  
            cout<<*it;  
        }  
        cout<<endl;  
        return;  
    }  
    if(*data=='\0')  
        return;  
    result.push_back(*data);  
    algorithm(data+1,num-1,result);  
    result.pop_back();  
    algorithm(data+1,num,result);  
}  
  
void main()  
{  
    char* data="abcd";  
    int length=strlen(data);  
    vector<char> result;  
    int i;  
    for(i=1;i<=length;i++)  
    {  
        algorithm(data,i,result);  
    }  
}