dfs 第2题

#include<bits/stdc++.h>
using namespace std;
const int N=20;
int a[N],vis[N];
int n,r;
int ans;
void dfs(int u) {
	if(u==r+1) {
		for(int i=1; i<=r; i++) {
			printf("%d",a[i]);
		}
		ans++;
		puts("");
		return;
	}
	for(int i=a[u-1]; i>=1; i--) {
		if(vis[i]==0) {
			vis[i]=1;
			a[u]=i;
			dfs(u+1);
			vis[i]=0;
		}
	}
}
int main() {
	freopen("b.in","r",stdin);
	freopen("b.out","w",stdout);
	scanf("%d %d",&n,&r);
	a[0]=n;
	dfs(1);
	printf("total=%d",ans);
	puts("");
	return 0;
}