HDU 4738 쌍 연통 모 판 문제

#include <string.h>   

#include <cstdio>

#include <vector>   

#define N 1010

#define inf 10000000

using namespace std;

inline int Min(int a,int b){return a>b?b:a;}

vector<int>G[N];

int dis[N][N],bian[N][N];

int n,m,f[N];

int find(int x){return x==f[x]?x:f[x]=find(f[x]);}

void Union(int u,int v){

    int fa=find(u),fb=find(v);

    f[fa]=fb;

}



struct node{

    int u,v,d;

}edge[N];//      n 

int edgenum;

void PUT(int u,int v,int d){

    node E={u,v,d};

    edge[edgenum++]=E;

}

int pre[N],low[N],dfs_clock;

bool su;

int dfs(int u,int fa){//    ,dfs(u, )     u        （     ） pre 

    if(su)return 0;

	int lowu=pre[u]= ++ dfs_clock;

    int child=0;

    for(int i=0;i<G[u].size();i++){

        int v=G[u][i];

        if(!pre[v])

		{

            child++;

            int lowv=dfs(v,u);

            lowu = Min(lowu, lowv);

			if(lowv > pre[u]&&bian[u][v]==1){PUT(u,v,dis[u][v]);if(dis[u][v]<=1)return 0;}

        }

        else if(pre[v] < pre[u] && v!=fa)

            lowu = Min(lowu, pre[v]);

    }

    return low[u]=lowu;

}

void findcut(){

    memset(pre,0,sizeof(pre));

    dfs_clock=0;

    dfs(1,-1);//dfs(  ，      -1) 

}

int main(){

    int i,u,v,d;

    while(scanf("%d %d",&n,&m),n)

    {

        memset(bian,0,sizeof(bian));

        for(i=1;i<=n;i++)

        {

            G[i].clear();

            f[i]=i;

            for(int j=1;j<=n;j++)

                dis[i][j]=inf;

        }



        while(m--)

        {

            scanf("%d %d %d",&u,&v,&d);

			if(dis[u][v]==inf)

			{

            G[u].push_back(v);       G[v].push_back(u);

            Union(u,v);

			}

            dis[u][v]=dis[v][u]=Min(dis[u][v],d);

            bian[u][v]++;            bian[v][u]++;

        }

     

        bool fa=false;	find(1);

        for(i=1;i<=n;i++)if(find(i)!=f[1]){fa=true;break;}

        if(fa){printf("0
");continue;}



		su=false;

		edgenum=0;

        findcut();



        if(edgenum)

        {

            int ans=inf;

            for(i=0;i<edgenum;i++)ans=Min(ans,edge[i].d);

            if(ans==inf)ans=-1;

            else if(ans==0)ans=1;

            printf("%d
",ans);

        }

        else printf("-1
");

    }

    return 0;

}

/* 

3 3 

1 2 7 

2 3 4 

3 1 4 

 

3 2 

1 2 7 

2 3 4 

 

3 4 

1 2 7 

2 1 7 

2 3 4 

3 2 4 

 

4 3 

1 2 1  

1 2 3 

3 4 4 

 

4 4 

1 2 1  

1 2 3 

3 4 4 

2 4 6 

 

4 5 

1 2 1  

1 2 3 

3 4 4 

2 4 6 

1 3 0 

 

4 5 

4 3 0 

3 4 4 

2 4 6 

2 3 0 

1 3 0 

 

2 1 

1 2 0 

 

4 2 

1 2 3 

1 3 5 

 

4 5 

1 2 3 

2 3 4 

1 3 5 

4 3 7 

4 3 6 

 

4 4 

1 2 3 

2 3 4 

1 3 5 

4 3 6 

 

4 4 

1 2 4 

1 3 5 

4 3 6 

3 4 7 

 

6 7 

1 2 1 

1 3 2 

2 3 3 

3 4 4 

4 6 5 

4 5 6 

5 6 7 

 

5 6 

1 2 3 

1 3 4 

2 3 5 

3 4 7 

3 5 8 

5 4 9 

 

8 9 

1 8 1 

5 1 2 

1 7 3 

1 4 4 

1 2 5 

4 3 6 

3 2 7 

5 6 8 

6 7 9 

 

6 6 

1 4 1 

1 2 4 

2 5 4 

5 6 4 

3 6 4 

4 3 2 

 

6 5 

1 2 4 

2 5 4 

5 6 4 

3 6 4 

4 3 2 

 

8 10 

1 8 1 

5 1 2 

1 7 3 

1 4 4 

1 2 5 

4 3 6 

3 2 7 

5 6 8 

6 7 9 

8 1 2 

 

3 3 

1 2 7 

1 3 1 

1 3 4 

 

0 0 

*/