Farm Tour(网络流模板题)

#include<cstdio>  
#include<cstring>  
struct edge{  
    int to,cap,rev,nx,we;  
}G[40050];  
int n,m,p;  
int h[2050],q[40050],d[2050];  
bool mark[2050];  
int Min(int a,int b){return a<b?a:b;}  
void ae(int s,int e,int c,int w){  
    G[++p]=(edge){e,c,p+1,h[s],w};h[s]=p;  
    G[++p]=(edge){s,0,p-1,h[e],-w};h[e]=p;  
}  
bool spfa(){  
    memset(d,127/3,sizeof(d));  
    memset(mark,0,sizeof(mark));  
    d[n+1]=0;mark[n+1]=1;  
    int head=0,tail=0;  
    int inf=d[0];  
    q[tail++]=n+1;  
    while(head!=tail){  
        int fr=q[head++];  
        for(int i=h[fr];i;i=G[i].nx){  
            if(G[G[i].rev].cap>0&&d[G[i].to]>d[fr]+G[G[i].rev].we){  
                d[G[i].to]=d[fr]+G[G[i].rev].we;  
                if(!mark[G[i].to])mark[G[i].to]=1,q[tail++]=G[i].to;  
            }  
        }  
        mark[fr]=0;  
    }  
    return !(d[0]==inf);  
}  
int dfs(int s,int t,int f){  
    mark[s]=1;  
    if(s==t) return f;  
    int sum=0;  
    for(int i=h[s];i;i=G[i].nx){  
        if(G[i].cap>0&&!mark[G[i].to]&&d[s]-G[i].we==d[G[i].to]){  
            int d=dfs(G[i].to,t,Min(G[i].cap,f));  
            if(d)sum+=d,f-=d,G[i].cap-=d,G[G[i].rev].cap+=d;  
            if(f==0)return sum;  
        }  
    }  
    return sum;  
}  
int m__f(){  
    int sum=0;  
    while(spfa()){  
        mark[n+1]=1;  
        while(mark[n+1]){  
            memset(mark,0,sizeof(mark));  
            sum+=dfs(0,n+1,99999999)*d[0];  
        }  
    }  
    return sum;  
}  
int main(){  
    scanf("%d%d",&n,&m);  
    for(int i=1;i<=m;i++){  
        int x,y,z;  
        scanf("%d%d%d",&x,&y,&z);  
        ae(x,y,1,z);ae(y,x,1,z);  
    }  
    ae(0,1,2,0);ae(n,n+1,2,0);  
    printf("%d\n",m__f());  
    return 0;  
}