思路：

对于递归的考察。类似于不断的二分枚举，总之考察的还是比较深入的，特别是用一个vector模拟栈的进出都是需要学习的地方。以后还需要仔细理解。

#include 
     
      #include 
      
       using namespace std;void SolveRecursively(char* s, int count, vector
       
        & result){    if (count == 0)    {        vector
        
         ::const_iterator iter;        for (iter = result.begin(); iter != result.end(); ++iter)            cout << *iter;        cout << endl;    }    else    {        if (*s == '\0')            return;        result.push_back(*s);        SolveRecursively(s + 1, count - 1, result);        result.pop_back();        SolveRecursively(s + 1, count, result);    }}void Combination(char* s){    if (s == nullptr)        return;    vector
         
           result;    int len = strlen(s);    for (int i = 1; i <= len; ++i)        SolveRecursively(s, i, result);}