BZOJ 3774 最优选择

翻转源汇比较容易写错。。。。要注意

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<queue>
#define maxn 55
#define maxv 10050
#define maxe 2000050
#define inf 1000000007
using namespace std;
int n,m,a[maxn][maxn],b[maxn][maxn],id[maxn][maxn][3],tot=0;
int s,t,dis[maxv],nume=1,ans=0,g[maxv];
queue <int> q;
struct edge
{
    int v,f,nxt;
}e[maxe];
void addedge(int u,int v,int f)
{
    e[++nume].v=v;e[nume].f=f;e[nume].nxt=g[u];g[u]=nume;
    e[++nume].v=u;e[nume].f=0;e[nume].nxt=g[v];g[v]=nume;
}
void build()
{
    s=0;t=++tot;
    for (int i=1;i<=n;i++)    
        for (int j=1;j<=m;j++)
        {                                
            if (!((i+j)&1))
            {
                addedge(s,id[i][j][1],a[i][j]);
                addedge(id[i][j][1],t,b[i][j]);addedge(s,id[i][j][2],b[i][j]);
                addedge(id[i][j][2],id[i][j][1],inf);
                if (i>1) addedge(id[i][j][2],id[i-1][j][1],inf);
                if (i<n) addedge(id[i][j][2],id[i+1][j][1],inf);
                if (j>1) addedge(id[i][j][2],id[i][j-1][1],inf);
                if (j<m) addedge(id[i][j][2],id[i][j+1][1],inf);
            }
            else
            {
                addedge(id[i][j][1],t,a[i][j]);
                addedge(s,id[i][j][1],b[i][j]);addedge(id[i][j][2],t,b[i][j]);
                addedge(id[i][j][1],id[i][j][2],inf);
                if (i>1) addedge(id[i-1][j][1],id[i][j][2],inf);
                if (i<n) addedge(id[i+1][j][1],id[i][j][2],inf);
                if (j>1) addedge(id[i][j-1][1],id[i][j][2],inf);
                if (j<m) addedge(id[i][j+1][1],id[i][j][2],inf);
            }
        }
}
bool bfs()
{
    for (int i=s;i<=t;i++) dis[i]=inf;dis[s]=0;
    q.push(s);
    while (!q.empty())
    {
        int head=q.front();q.pop();
        for (int i=g[head];i;i=e[i].nxt)
        {
            int v=e[i].v;
            if (dis[v]>dis[head]+1 && e[i].f>0)
            {
                dis[v]=dis[head]+1;
                q.push(v);
            }
        }
    }
    return dis[t]!=inf;
}
int dinic(int x,int low)
{
    if (x==t) return low;
    int ret=0;
    for (int i=g[x];i && low;i=e[i].nxt)
    {
        int v=e[i].v;
        if (e[i].f>0 && dis[v]==dis[x]+1)
        {
            int dd=dinic(v,min(low,e[i].f));
            ret+=dd;low-=dd;e[i].f-=dd;e[i^1].f+=dd;
        }
    }
    if (!ret) dis[x]=inf;
    return ret;
}
int main()
{
    scanf("%d%d",&n,&m);
    for (int i=1;i<=n;i++)
        for (int j=1;j<=m;j++)
            scanf("%d",&a[i][j]);
    for (int i=1;i<=n;i++)
        for (int j=1;j<=m;j++)
        {
            scanf("%d",&b[i][j]);ans+=2*b[i][j];
            id[i][j][1]=++tot;
        }
    for (int i=1;i<=n;i++)
        for (int j=1;j<=m;j++)
            id[i][j][2]=++tot;
    build();
    while (bfs()) 
        ans-=dinic(s,inf);
    printf("%d\n",ans);
    return 0;
}