按字典序排列，只要先选先输出就好

#include <iostream>
#include <algorithm>
#include <vector>

using namespace std;

int n,m;
vector<int> choose;

void calc(int x)
{
    if(n - x + 1 < m - choose.size()) return ;
    if(m == choose.size())
    {
        for(int i = 0; i < m; i++)
            printf("%d ",choose[i]);
        puts("");
        return ;
    }
    if(x == n + 1) return ;

    //选
    choose.push_back(x);
    calc(x + 1);
    choose.pop_back();//准备回溯到上一问题之前，还原现场。
    //不选
    calc(x + 1);

}

int  main()
{
    cin>>n>>m;
    calc(1);
}