P2774 方格取数问题

#include<iostream>
#include<algorithm>
#include<cstring>
#include<queue>
#define IOS std::ios::sync_with_stdio(0)
using namespace std;
const int  N=1e4,M=5e5;
 #define inf 1e9 
 int n,m,B,W,a[N][N],id[102][102];
 
 int all=1,hd[N],go[M],w[M],nxt[M];
   
 int S,T;
 int dis[M],ans=0,now[M];
   
 void add_(int x,int y,int z){
     nxt[++all]=hd[x]; hd[x]=all; go[all]=y;
     w[all]=z;
     swap(x,y);
     nxt[++all]=hd[x]; hd[x]=all; go[all]=y;
     w[all]=0;
 }
  bool bfs(){
     for(int i=0;i<M;i++)dis[i]=inf;
     queue<int> q;
     q.push(S);
     now[S]=hd[S];
     dis[S]=0;
       
     while(q.empty()==0){
         int x=q.front();
         q.pop();
         for(int i=hd[x];i;i=nxt[i]){
             int y=go[i];
             if(w[i]>0&&dis[y]==inf){
                 dis[y]=dis[x]+1;
                 now[y]=hd[y];
                 q.push(y);
                 if(y==T) return 1;
             }
         }
     }
     return 0;
 }
 int dfs(int x,int sum){
     if(x==T) return sum;
     int k,res=0;
       
     for(int i=now[x];i&& sum ;i=nxt[i]){
         now[x]=i;
         int y=go[i];
         if(w[i]>0&&(dis[y]==dis[x]+1)){
             k=dfs(y,min(sum,w[i]));
             if(k==0) dis[y]=inf;
             w[i]-=k;
             w[i^1]+=k;
             res+=k;
             sum-=k;
         }
     }
     return res;
 }
 int dx[4]={-1,1,0,0},dy[4]={0,0,1,-1} ,SUM=0,col[102][102];
 int ID(int x,int y){
 	return (x-1)*m+y;
 }
 bool ok(int x,int y){
 	return x>0&&x<=n&&y>0&&y<=m;
 }
 void dinic(){
 	int ans =0;
 	while(bfs()) ans+=dfs(S,inf);	
 	cout<<SUM-ans<<endl;
 }
 
 signed main(){
    cin>>n>>m;
    int i,j;
    for(i=1;i<=n;i++)
     for(j=1;j<=m;j++) cin>>a[i][j],SUM+=a[i][j]; 
    
    S=0,T=n*m+1;
    for(i=1;i<=n;i++) 
    	for(j=1;j<=m;j++){
    		id[i][j]= m*(i-1)+j; col[i][j]=(i+j)%2;
    	}
    		
    for(i=1;i<=n;i++)
     for(j=1;j<=m;j++)
	      if(col[i][j]){
	      	add_(S,id[i][j],a[i][j]);
	      	for(int k=0;k<4;k++) { 
	      		int xx=i+dx[k],yy=j+dy[k];
	      		if(ok(xx,yy))
	      	    	add_(id[i][j],id[xx][yy],inf);
	      	}	
	      }
      for(i=1;i<=n;i++)
	     for(j=1;j<=m;j++)
		      if(col[i][j]==0){
		      	add_(id[i][j],T,a[i][j]);
		      }	
    dinic();
 }