改了一个小错误，但还是只有 18 分
```cpp
#include<bits/stdc++.h>
using namespace std;
const int size=1e6+10;
const int inf=0x3f3f3f3f;
int m,n,a[110][110],S,T,sum=0;
int dx[]={-1,0,1,0};
int dy[]={0,-1,0,1};
inline int encode(int x,int y){return (x-1)*n+y;}
int ver[size],edge[size],nxt[size],head[size],tot=1,d[size],maxflow=0;
inline void add(int x,int y,int z){
ver[++tot]=y;edge[tot]=z;nxt[tot]=head[x];head[x]=tot;
ver[++tot]=x;edge[tot]=0;nxt[tot]=head[y];head[y]=tot;
}
inline bool bfs(){
queue<int> q;
while(!q.empty()) q.pop();
memset(d,0,sizeof(d));
q.push(S);d[S]=1;
while(!q.empty()){
int x=q.front();q.pop();
for(int i=head[x];i;i=nxt[i]){
int y=ver[i],z=edge[i];
if(z&&(!d[y])){
d[y]=d[x]+1;
q.push(y);
if(y==T) return 1;
}
}
}
return 0;
}
int dinic(int x,int flow){
if(x==T) return flow;
int used=0;
for(int i=head[x];i;i=nxt[i]){
int y=ver[i],z=edge[i];
if(d[y]==d[x]+1&&z&&used<flow){
int now=dinic(y,min(flow,z));
used+=now;
edge[i]-=now;
edge[i^1]+=now;
}
}
if(!used) d[x]=0;
return used;
}
int main(){
ios::sync_with_stdio(0);
cin>>m>>n;
S=0;T=m*n+1;
for(int i=1;i<=m;++i) for(int j=1;j<=n;++j) cin>>a[i][j],sum+=a[i][j];
for(int i=1;i<=m;++i) for(int j=1;j<=n;++j) ((i+j)%2==0)?add(encode(i,j),T,a[i][j]):add(S,encode(i,j),a[i][j]);
for(int i=1;i<=m;++i) for(int j=1;j<=n;++j) if((i+j)&1) for(int k=0;k<4;++k) if(i+dx[k]<=m&&i+dx[k]>=1&&j+dy[k]<=n&&j+dy[k]>=1) add(encode(i,j),encode(i+dx[k],j+dy[k]),inf);
int flow;
while(bfs()) while(flow=dinic(S,inf)) maxflow+=flow;
cout<<sum-maxflow<<endl;
return 0;
}
```
by Belarus @ 2020-07-26 08:32:58