Acwing 93

#include <iostream>
using namespace std;
const int N = 16;
bool record[N];
void selection(int start, int end,int capacity,int num) {
    if(num == capacity){
        for(int i = 1;i <= end;i++){
            if(record[i]) cout<<i<<" ";
        }
        cout<<endl;
        return;
    }
    if(start>end){  //到达上届
        return;
    }
    record[start] = true;   //选
    selection(start + 1,end,capacity,num+1);
    record[start] = false;  //不选
    selection(start + 1,end,capacity,num);
}
int main(){
    int n = 0,c = 0;
    cin>>n>>c;
    selection(1,n,c,0);
    return 0;
}