P2774 方格取数问题

/*Code by 520 -- 8.25*/
#include<bits/stdc++.h>
#define il inline
#define ll long long
#define RE register
#define For(i,a,b) for(RE int (i)=(a);(i)<=(b);(i)++)
#define Bor(i,a,b) for(RE int (i)=(b);(i)>=(a);(i)--)
#define debug printf("%d %s\n",__LINE__,__FUNCTION__)
using namespace std;
const int N=100005,inf=233333333,dx[4]={0,0,1,-1},dy[4]={1,-1,0,0};
int n,m,s,t,dis[N],to[N],net[N],w[N],h[N],cnt=1;
int mp[105][105],ans;

il int id(int x,int y){return (x-1)*m+y;}

il void add(int u,int v,int c){
    to[++cnt]=v,net[cnt]=h[u],w[cnt]=c,h[u]=cnt;
    to[++cnt]=u,net[cnt]=h[v],w[cnt]=0,h[v]=cnt;
}

queue<int>q;
il bool bfs(){
    memset(dis,-1,sizeof(dis));
    q.push(s),dis[s]=0;
    while(!q.empty()){
        RE int u=q.front();q.pop();
        for(RE int i=h[u];i;i=net[i])
            if(dis[to[i]]==-1&&w[i]) dis[to[i]]=dis[u]+1,q.push(to[i]);
    }
    return dis[t]!=-1;
}

int dfs(int u,int op){
    if(u==t)return op;
    int flow=0,used=0;
    for(RE int i=h[u];i;i=net[i]){
        int v=to[i];
        if(dis[to[i]]==dis[u]+1&&w[i]){
            used=dfs(to[i],min(op,w[i]));
            if(!used)continue;
            flow+=used,op-=used;
            w[i]-=used,w[i^1]+=used;
            if(!op)break;
        }
    }
    if(!flow) dis[u]=-1;
    return flow;
}

il void init(){
    scanf("%d%d",&n,&m),t=n*m+1;
    For(i,1,n) For(j,1,m) {
        scanf("%d",&mp[i][j]),ans+=mp[i][j];
        (i+j)&1?add(s,id(i,j),mp[i][j]):add(id(i,j),t,mp[i][j]);    
    }
    For(i,1,n) For(j,1,m)
        if((i+j)&1) {
            For(k,0,3){
                RE int xx=i+dx[k],yy=j+dy[k];
                if(xx>0&&xx<=n&&yy>0&&yy<=m) add(id(i,j),id(xx,yy),inf);
            }
        }
    while(bfs()) ans-=dfs(s,inf);
    cout<<ans;
}

int main(){
    init();
    return 0;
}