RT，这样卡是否有些离谱了……

或者说有没有人能给蒟蒻一点卡常的建议？

代码如下：

#include<iostream>
#include<cstdio>
#include<cstring>
#include<queue>
using namespace std;
const int inf=1<<30;
int fx[8][2]={{2,1},{2,-1},{1,2},{1,-2},{-2,1},{-2,-1},{-1,2},{-1,-2}};
int n,m,x,y,s,t,tot=1,bj[201][201],fir[40005],nxt[1000001],to[1000001],cap[1000001],flow[1000001],pre[40005],h[40005],hsl[40005];
queue<int> q;
int ch(int i,int j){return (i-1)*n+j;}
void ins(int x,int y,int v)
{
	nxt[++tot]=fir[x];
	fir[x]=tot;
	to[tot]=y;
	cap[tot]=v;
}
void seth(int t)
{
	memset(h,-1,sizeof(h));
	q.push(t);h[t]=0;
	while(!q.empty())
	{
		int now=q.front();q.pop();
		hsl[h[now]]++;
		for(int i=fir[now];i;i=nxt[i])
			if(h[to[i]]==-1)
			{
				h[to[i]]=h[now]+1;
				q.push(to[i]);
			}
	}
}
int ISAP(int s,int t)
{
	seth(t);
	int now=s,ans=0,d=1<<30;
	while(h[s]<n*n+2)
	{
		if(now==s) d=1<<30;
		int i=fir[now];
		for(;i;i=nxt[i])
			if(cap[i]>flow[i]&&h[now]==h[to[i]]+1)
			{
				d=min(d,cap[i]-flow[i]);
				now=to[i];pre[to[i]]=i;
				if(now==t)
				{
					while(now!=s)
					{
						int k=pre[now];
						flow[k]+=d;flow[k^1]-=d;
						now=to[k^1];
					}
					ans+=d;d=1<<30;
				}
				break;
			}
		if(!i)
		{
			if(--hsl[h[now]]==0) break;
			int minh=n*n+1;
			for(int j=fir[now];j;j=nxt[j])
				if(cap[j]>flow[j]) minh=min(minh,h[to[j]]);
			h[now]=minh+1;
			hsl[h[now]]++;
			if(now!=s) now=to[pre[now]^1];
		}
	}
	return ans;
}
int main()
{
	scanf("%d%d",&n,&m);s=n*n+1,t=s+1;
	for(int i=1;i<=m;i++)
	{
		scanf("%d%d",&x,&y);
		bj[x][y]=1;
	}
	for(int i=1;i<=n;i++)
		for(int j=1;j<=n;j++)
		{
			if(bj[i][j]) continue;
			int cur=ch(i,j);
			if((i+j)%2==0)
			{
				ins(s,cur,1),ins(cur,s,0);
				for(int l=0;l<8;l++)
				{
					int ni=i+fx[l][0],nj=j+fx[l][1],np=ch(ni,nj);
					if(ni>=1&&nj>=1&&ni<=n&&nj<=n&&!bj[ni][nj])
						ins(cur,np,inf),ins(np,cur,0);
				}
			}
			else ins(cur,t,1),ins(t,cur,0);
		}
	printf("%d",n*n-m-ISAP(s,t));
	return 0;
}