ZOJ 3687 The Review Plan I 容斥原理/禁位排列

#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;

#define MOD 55566677
#define lint long long
#define MAXN 52

int fa[MAXN];
int n, m;
int a[MAXN][2];
bool ban[MAXN][MAXN];
bool vis1[MAXN], vis2[MAXN];
int ret;

void init()
{
fa[0] = 1;
for(int i = 1; i <= 50; i++)
fa[i] = ((lint)fa[i-1] * i) % MOD;

// for(int i = 1; i <= 50; i++)
//     printf("%d\n", fa[i]);
}

void In_Exclusion(int i, int num) //i表示第i个条件，num表示条件数目
{
if(i > m)
{
if(num & 1) ret = (ret - fa[n-num]) % MOD;
else ret = (ret + fa[n-num]) % MOD;
return;
}

In_Exclusion(i + 1, num); //第i个条件不用
if(vis1[a[i][0]] == false && vis2[a[i][1]] == false)
{
vis1[a[i][0]] = vis2[a[i][1]] = true;
In_Exclusion(i + 1, num + 1);
vis1[a[i][0]] = vis2[a[i][1]] = false;
}
}

int main()
{
init();
while(scanf("%d%d",&n,&m) != EOF)
{
memset(ban, 0, sizeof(ban));
memset(vis1, 0, sizeof(vis1));
memset(vis2, 0, sizeof(vis2));

for(int i = 1; i <= m; i++)
{
scanf("%d%d", &a[i][0], &a[i][1]);
if(ban[a[i][0]][a[i][1]] == false)
ban[a[i][0]][a[i][1]] = true;
else {m--, i--;}
}

ret = 0;
In_Exclusion(1, 0);
printf("%d\n", (ret % MOD + MOD) % MOD);
}
return 0;
}