题解

#include <bits/stdc++.h>
using namespace std;
bool used[19];
int p[19], n, r;
void dfs(int idx)
{
	if(idx == r + 1)
	{
		for(int i = 1; i <= r; i++)
		{
			cout << " " << p[i];
		}
		cout << endl;
		return;
	}
	for(int i = p[idx - 1] + 1; i <= n ; i++)
	{
		if(!used[i])
		{
			p[idx] = i;
			used[i] = true;
			dfs(idx + 1);
			p[idx] = 0;
			used[i] = false;
		}
	}
}
int main() 
{
	cin >> n >> r;
	dfs(1);
	return 0;
}