ZOJ 3687 The Review Plan I 解题报告

//Time:320ms
//Memory:180KB
//Length:1090B
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <algorithm>
using namespace std;
#define MAXN 60
#define MOD 55566677
int ans;
int pre[MAXN],jie[MAXN];
int a[MAXN],b[MAXN];
int n,m;
void dfs(int h,int cnt,int ty)
{
if(h==m)
{
ans=(ans+(cnt%2?-1:1)*jie[n-cnt]+MOD)%MOD;
return ;
}
dfs(h+1,cnt,ty);
if(!(pre[h]&ty))
dfs(h+1,cnt+1,ty|(1<<h));
}
int main()
{
//freopen("/home/moor/Code/input","r",stdin);
jie[0]=1;
for(int i=1;i<MAXN;++i)   jie[i]=(long long)jie[i-1]*i%MOD;
bool flag;
while(scanf("%d%d",&n,&m)==2)
{
for(int i=0;i<m;++i)
{
flag=0;
scanf("%d%d",&a[i],&b[i]);
pre[i]=0;
for(int j=0;j<i;++j)
{
int cnt=0;
cnt+=(a[i]==a[j]);
cnt+=(b[i]==b[j]);
if(cnt==1)  pre[i]|=1<<j;
else    if(cnt==2)  flag=1;
}
if(flag)   --i,--m;
}
ans=0;
dfs(0,0,0);
printf("%d\n",ans);
}
return 0;
}