网络流24题-方格取数

  1 #include <algorithm>
  2 #include <iostream>
  3 #include <cstring>
  4 #include <cstdlib>
  5 #include <cstdio>
  6 #include <vector>
  7 #include <cmath>
  8 #include <queue>
  9 #include <map>
 10 #include <set>
 11 using namespace std;
 12 
 13 inline void read(int &ans){
 14   ans=0;char x=getchar();int f=1;
 15   while(x<‘0‘||x>‘9‘){if(x==‘-‘)f=-1;x=getchar();}
 16   while(x>=‘0‘&&x<=‘9‘)ans=ans*10+x-‘0‘,x=getchar();
 17   ans*=f;
 18 }
 19 const int MAXN=30+10;
 20 const int MAXV=MAXN*MAXN;
 21 const int MAXE=MAXV<<4;
 22 const int INF=2e9;
 23 struct net{int v,next,c;}E[MAXE];
 24 int head[MAXV],tot,n,m;
 25 int vis[MAXN][MAXN],val[MAXN][MAXN],cnt;
 26 void edge(int u,int v,int c){
 27   E[tot]=(net){v,head[u],c},head[u]=tot++;
 28   E[tot]=(net){u,head[v],0},head[v]=tot++;
 29 }
 30 struct Net{
 31   int s,t;
 32   int dep[MAXV],cur[MAXV];
 33   void init(int a,int b){
 34     s=a,t=b,memset(head,-1,sizeof(head));
 35   }
 36   bool bfs(){
 37     memset(dep,0,sizeof(dep));
 38     queue<int>q;
 39     dep[s]=1,q.push(s);
 40     while(!q.empty()){
 41       int u=q.front();q.pop();
 42       for(int i=head[u];~i;i=E[i].next){
 43     int v=E[i].v;
 44     if(!dep[v]&&E[i].c>0){
 45       dep[v]=dep[u]+1;
 46       q.push(v);
 47     }
 48       }
 49       if(dep[t])return true;
 50     }
 51     return false;
 52   }
 53   int dfs(int u,int f){
 54     if(u==t)return f;
 55     int ans=0,cup;
 56     for(int &i=cur[u];~i;i=E[i].next){
 57       int v=E[i].v;
 58       if(E[i].c>0&&dep[v]==dep[u]+1){
 59     cup=dfs(v,min(f-ans,E[i].c));
 60     E[i].c-=cup;
 61     E[i^1].c+=cup;
 62     ans+=cup;
 63     if(ans==f)return ans;
 64       }
 65     }
 66     return ans;
 67   }
 68   int work(){
 69     int ans=0;
 70     while(bfs()){
 71       for(int i=0;i<=t;i++)cur[i]=head[i];
 72       ans+=dfs(s,INF);
 73     }
 74     return ans;
 75   }
 76 }a;
 77 
 78 int Tx[4]={1,-1,0,0};
 79 int Ty[4]={0,0,-1,1};
 80 int main(){
 81   read(n),read(m);
 82   int s=n*m+1,t=s+1;
 83   a.init(s,t);
 84   for(int i=1;i<=n;i++)
 85     for(int j=1;j<=m;j++)
 86       read(val[i][j]),vis[i][j]=++cnt;
 87   int SUM=0;
 88   for(int i=1;i<=n;i++)
 89     for(int j=1;j<=m;j++){
 90       SUM+=val[i][j];
 91       if((i+j)&1)edge(s,vis[i][j],val[i][j]);
 92       else       edge(vis[i][j],t,val[i][j]);
 93       int I,J;
 94       if((i+j)&1)
 95     for(int k=0;k<4;k++){
 96       I=i+Tx[k],J=j+Ty[k];
 97       if(I<1||I>n||J<1||J>m)continue;
 98       edge(vis[i][j],vis[I][J],INF);
 99     }
100     }
101   cout<<SUM-a.work()<<endl;
102   return 0;
103 }