程序代码：

char* Permutation(char* pStr, char* pBegin,char *s,int num) 
{ 
    assert(pStr && pBegin);
    int j;
    if(*pBegin == '\0') 
    {
        for(j=0;j<num;j++)
        {
            s[k++]=pStr[j];
        }
    }
    else 
    { 
        for(char* pCh = pBegin; *pCh != '\0'; pCh++) 
        { 
            swap(*pBegin,*pCh); 
            Permutation(pStr, pBegin+1,s,num); 
            swap(*pBegin,*pCh); 
        } 
    }
    return s;
}