易错点：
- 八倍开边，
我真的没有开挂. - 只有坐标不越界的点集才是好同志.
- 支持相互match这个一定要好评.
#include<cstdio>
#include<iostream>
#include<cstring>
using namespace std;
const int MAXN=120*120;
int dx[8]={-2,-2,-1,-1,1,1,2,2},dy[8]={1,-1,2,-2,2,-2,1,-1};
struct Edge{
int from,to,nxt;
}e[MAXN*8];
int head[MAXN],edgeCnt=1;
void addEdge(int u,int v){
e[++edgeCnt].from=u;
e[edgeCnt].to=v;
e[edgeCnt].nxt=head[u];
head[u]=edgeCnt;
}
int vis[MAXN],match[MAXN];
bool dfs(int x){
for(int i=head[x];i;i=e[i].nxt){
int nowV=e[i].to;
if(vis[nowV])continue;
vis[nowV]=1;
if(!match[nowV]||dfs(match[nowV])){
match[nowV]=x;
match[x]=nowV;
return 1;
}
}
return 0;
}
int m;
int getHash(int i,int j){
return (i-1)*m+j;
}
int a[120][120];
int main(){
int n,t;
scanf("%d%d%d",&n,&m,&t);
for(int i=1;i<=t;i++){
int x,y;
scanf("%d%d",&x,&y);
a[x][y]=1;
}
for(int x=1;x<=n;x++)
for(int y=1;y<=m;y++){
if(a[x][y])continue;
int nowU=getHash(x,y);
for(int k=0;k<=7;k++){
int nowX=x+dx[k],nowY=y+dy[k];
if(nowX<1||nowX>n||nowY<1||nowY>m)continue;
if(a[nowX][nowY])continue;
int nowV=getHash(nowX,nowY);
addEdge(nowU,nowV);
}
}
int k=0,pointCnt=n*m;
for(int i=1;i<=pointCnt;i++){
if(match[i])continue;
memset(vis,0,sizeof(vis));
k+=dfs(i);
}
int ans=n*m-t-k;
printf("%d
",ans);
return 0;
}