#include <iostream>
#include <stack>
using namespace std;

int total = 0;

struct STATE
{
    int        curr;
    int        min;
    int        mark;
    STATE(int c = 0, int mi = 0, int ma = 0) : curr(c), min(mi), mark(ma){}
};

void select(char* str, char* buff, int    l, int n)
{
    stack<STATE>    stk;
    STATE            t;
    buff[n] = 0;
    stk.push(STATE());

    if (n == 0)
    {
        cout << endl;
        total++;
        return;
    }
    while (!stk.empty())
    {
        t = stk.top();
        stk.pop();
        if (t.curr == n - 1)
        {
            for (int i = t.min; i < l; i++)
            {
                buff[t.curr] = str[i];
                cout << buff << endl;
                total++;
            }
        }
        else if (t.mark == 0)
        {
            t.mark = 1;
            stk.push(t);
            buff[t.curr] = str[t.min];
            stk.push(STATE(t.curr + 1, t.min + 1, 0));
        }
        else
        {
            if (t.min + 1 < l)
                stk.push(STATE(t.curr, t.min + 1, 0));
        }
    }
}

int    main(void)
{
    char str[]="abcdefg";
    char buffer[32];

    total = 0;
    select(str, buffer, strlen(str), 3);
    cout << total << endl;

    return 0;
}

#include <iostream>
using namespace std;

void    comb(int l, int last, int m, int n, char* data)
{
    if (l == n)
    {
        for (int i = 0; i < n; i++)
            cout<<data[i];
        cout<<endl;
        return;
    }
    else
    {
        for (int i = last; i < m; i++)
        {
            data[l] = i + 'A';
            comb(l + 1, i + 1, m, n, data);
        }
    }
}

int    main()
{
    int    m, n;
    char    data[32];

    cout<<"input m n:";
    cin>>m>>n;
    comb(0, 0, m, n, data);

    return 0;
}

#include <iostream>
using namespace std;

#include <stdio.h>
#define MAX 20
void comb_origin( int a[], int b[], int n, int m, const int M, int *count)
{
     int i,j;
     for(i = n; i>=m; i--)
     {
           b[m-1] = i - 1;
                  if(m > 1)
                       comb_origin(a, b, i-1, m-1, M, count);
                  else
                  {   
                       for(j = M-1; j>=0; j--)
                             printf("%d ",a[b[j]]);
                       printf("\n");
                       (*count)++;
                  }
     }
}
int combine(int A[], int N, int M)//从A中N个元素中取M个 
{
     int B[MAX];
     static int Count = 0;
     comb_origin(A, B, N, M, M, &Count);
     return Count;
}
 
int main()
{
    int set[9] = {1,2,3,4,5,6,7,8,9};
    int c = combine(set,9,5); //从集合set中的9个元素里选5个元素的组合 
    printf("\n 共%d组 \n",c);
    
    system("PAUSE");
    return 0;
}