POJ1637[Sightseeing tour]

混合图的欧拉回路,用网络流做。


CODE:


/*


AUTHOR: Su Jiao


DATE: 2010-7-21


DESCRIPTION:


网络流 乱做


http://acm.pku.edu.cn/JudgeOnline/problem?id=1637


*/


#include <stdio.h>


#include <string.h>


 


const int oo=(~0u)>>1;


const int MAXV=1102;


const int MAXE=6200;


typedef struct struct_edge* edge;


struct struct_edge{int v,c;edge n,b;};


struct_edge pool[MAXE];


edge top;


int S,T,V;


edge adj[MAXV];


int d[MAXV];


int q[MAXV];


int head,tail;


void add_edge(int u,int v,int c)


{


     top->v=v,top->c=c,top->n=adj[u],adj[u]=top++;


     top->v=u,top->c=0,top->n=adj[v],adj[v]=top++;


     adj[u]->b=adj[v],adj[v]->b=adj[u];


}


bool relabel()


{


     for (int i=0;i<V;d[i++]=oo) ;


     d[q[head=tail=0]=T]=0;


     while (head<=tail)


     {


           int u=q[head++];


           for (edge i=adj[u];i;i=i->n)


               if (i->b->c&&d[i->v]==oo)


                  d[q[++tail]=i->v]=d[u]+1;


           if (d[S]!=oo) return true;


     }


     return false;


}


int augment(int u,int e)


{


    if (u==T) return e;


    int f=0;


    for (edge i=adj[u];i&&e;i=i->n)


        if (i->c&&d[u]==d[i->v]+1)


           if (int df=augment(i->v,e<i->c?e:i->c))


              i->c-=df,i->b->c+=df,e-=df,f+=df;


    return f;


}


int dinic()


{


    int f=0;


    while (relabel()) f+=augment(S,oo);


    return f;


}


 


const int SIZE=1000;


int n,m,s,a[SIZE],b[SIZE],c[SIZE];


int degree[SIZE];


int main()


{


    scanf(“%d”,&n);


    for (int t=0;t<n;t++)


    {


        scanf(“%d%d”,&m,&s);


        memset(degree,0,sizeof(degree));


        for (int i=0;i<s;i++)


            scanf(“%d%d%d”,a+i,b+i,c+i),


            degree[a[i]]++,degree[b[i]]–;


        top=pool;


        memset(adj,0,sizeof(adj));


        S=0,T=m+1,V=m+2;


        int total=0;


        bool no_solution=false;


        for (int i=1;i<=m;i++)


        {


            if (degree[i]&1) no_solution=true;


            if (degree[i]>0) add_edge(S,i,degree[i]>>1),total+=degree[i]>>1;


            else add_edge(i,T,(-degree[i])>>1);


        }


        for (int i=0;i<s;i++)


            if (!c[i]) add_edge(a[i],b[i],1);


        if (no_solution||dinic()!=total) printf(“im”);


        printf(“possible\n”);


    }


}