强连通专题

#include<stdio.h>
#include<string.h>
#include<algorithm>
using namespace std;
const int MN=1111;

struct Edge
{
   int to,next;
}edge[MN<<2];

int dfn[MN];
int low[MN];
int head[MN<<2];
int subnet[MN];
int E,tp,root;
int vis[MN];

void Init()
{
    memset(dfn,-1,sizeof(dfn));
    memset(low,0,sizeof(low));
    memset(head,-1,sizeof(head));
    memset(subnet,0,sizeof(subnet));
    memset(vis,0,sizeof(vis));
    E=tp=0;
}

void Add(int a,int b)
{
    edge[E].to=b;
    edge[E].next=head[a];
    head[a]=E++;
}

void tarjan(int u,int fa)
{
    int son=0;
    vis[u]=1;
    dfn[u]=low[u]=++tp;
    for(int i=head[u];i!=-1;i=edge[i].next)
    {
        int v=edge[i].to;
        if(vis[v]==1 && v!=fa)
           low[u]=min(low[u],dfn[v]);
        if(!vis[v])
        {
            tarjan(v,u);
            son++;
            low[u]=min(low[u],low[v]);
            if((u==root && son>1) || (u!=root)&& dfn[u]<=low[v])
              subnet[u]++;
        }
    }
    vis[u]=2;
}
int main()
{
    int i,cas=1,n,a,b,nodes;
    while(scanf("%d",&n) && n)
    {
        nodes=n;
        Init();
        scanf("%d",&b);
        Add(n,b);
        Add(b,n);
        while(scanf("%d",&a) && a)
        {
            scanf("%d",&b);
            if(nodes<a) nodes=a;
            if(nodes<b) nodes=b;
            Add(a,b);
            Add(b,a);
        }
        for(i=1;i<=nodes;i++)
        {
            if(dfn[i]==-1)
            {
                 root=i;
                 tarjan(i,-1);
            }
        }
        int flag=0;
        printf("Network #%d\n",cas++);
        for(i=1;i<=nodes;i++)
        {
            if(subnet[i]>=1)
            {
                flag=1;
                printf("  SPF node %d leaves %d subnets\n",i,subnet[i]+1);
            }
        }
        if(flag==0)  printf("  No SPF nodes\n");
        puts("");
    }
}

#include<stdio.h>
#include<string.h>
#include<algorithm>
using namespace std;
const int MN=1010;
int dfn[MN],low[MN],num[MN];
int vis[MN],ww[MN*MN];
int tp,E;
int ans,cnt;

struct Edge
{
    int next,to;
    int tag;//判断是否有重边
    int pos;//第几条边
    int w;
} edge[MN*MN];
int head[MN*MN];
int bridge[MN*MN];

void init()
{
    memset(dfn,-1,sizeof(dfn));
    memset(low,0,sizeof(low));
    memset(head,-1,sizeof(head));
    memset(vis,0,sizeof(vis));
    E=tp=0;
}

int Add(int a,int b,int pos,int c)
{
    for(int i=head[a]; i!=-1; i=edge[i].next)
    {
        if(edge[i].to==b)
        {
            edge[i].tag++;
            return true;
        }
    }
    edge[E].tag=0;
    edge[E].w=c;
    edge[E].pos=c;
    edge[E].to=b;
    edge[E].next=head[a];
    head[a]=E++;
}

void tarjan(int u,int fa)
{
    dfn[u]=low[u]=++tp;
    vis[u]=1;
    for(int i=head[u]; i!=-1; i=edge[i].next)
    {
        int v=edge[i].to;
        if(v==fa) continue;
        if(!vis[v])
        {
            tarjan(v,u);
            low[u]=min(low[u],low[v]);
            if(low[v]>dfn[u] && !edge[i].tag)
            {
                ww[++ans]=edge[i].w;
            }
        }
        else
            low[u]=min(low[u],dfn[v]);
    }
}

int main()
{
    int T,n,m,a,b,c;
    while(scanf("%d%d",&n,&m))
    {
        if(n==0 && m==0) break;
        init();
        for(int i=1; i<=m; i++)
        {
            scanf("%d%d%d",&a,&b,&c);
            Add(a,b,i,c);
            Add(b,a,i,c);
        }
        ans=0;
        tarjan(1,-1);
        cnt=0;
        for(int j=1; j<=n; j++)
        {
            if(!vis[j]) cnt++;
        }
        if(cnt) printf("0\n");
        else
        {
            if(ans)
            {
                int MIN=99999999;
                for(int i=1; i<=ans; i++)
                {
                    if(MIN>ww[i]) MIN=ww[i];
                }
                if(MIN==0) printf("1\n");
                else printf("%d\n",MIN);
            }
            else printf("-1\n");
        }

    }
    return 0;
}

#include<stdio.h>
#include<string.h>
#include<algorithm>

using namespace std;

const int MN=5010;
const int MM= 10011;

int low[MN],dfn[MN];
int instack[MM];
int subnet[MN],vis[MN];
int stap[MN],head[MM];
int degree[MN];
int belong[MN];
int tp,root;
int E,p;
int ans;
int cnt;

struct Edge
{
    int to,next;
} edge[MM];

void Addedge(int a,int b)
{
    for(int i=head[a]; i!=-1; i=edge[i].next)
    {
        if(edge[i].to==b)
        {
            return ;
        }
    }
    edge[E].to=b;
    edge[E].next=head[a];
    head[a]=E++;
}

void Init()
{
    memset(dfn,-1,sizeof(dfn));
    memset(low,0,sizeof(low));
    memset(head,-1,sizeof(head));
    memset(degree,0,sizeof(degree));
    memset(instack,0,sizeof(instack));
    memset(belong,-1,sizeof(belong));
    tp=E=p=0;
    ans=cnt=0;
}

void tarjan(int x,int fa)
{
   low[x]=dfn[x]=++tp;
   stap[++p]=x;
   instack[x]=1;
   for(int i=head[x];i!=-1;i=edge[i].next)
   {
       int v=edge[i].to;
       if(v==fa) continue;
       if(dfn[v]==-1)
       {
           tarjan(v,x);
           if(low[x]>low[v])
              low[x]=low[v];
       }
       else if(instack[v] && dfn[v]<low[x])
          low[x]=dfn[v];
   }
   if(low[x]==dfn[x])
   {
       int top;
       do
       {
          top=stap[p];
          instack[top]=0;
          belong[top]=cnt;
          p--;
       }
       while(x!=top);
       cnt++;
   }
}

int main()
{
    char s[100];
    int i,j,n,m,a,b;
    int cas=1;
    while(scanf("%d%d",&n,&m)!=EOF)
    {
        Init();
        for(i=1; i<=m; i++)
        {
            scanf("%d%d",&a,&b);
            Addedge(a,b);
            Addedge(b,a);
        }
        for(i=1; i<=n; i++)
        {
            if(dfn[i]==-1)
            {
                tarjan(i,-1);
            }
        }
        for(i=1;i<=n;i++)
        {
            for(j=head[i];j!=-1;j=edge[j].next)
            {
                int x=belong[i];
                int y=belong[edge[j].to];
                if(x!=y)//当x和y不属于同一个缩点的时候
                {
                    degree[x]++;
                    degree[y]++;
                }
            }
        }
        int res=0;
        for(i=0;i<cnt;i++)//由于无向图每个点的度加了两次
        {//当度是1的时候表明是叶子节点
            if(degree[i]/2==1) res++;
        }
       // printf("Output for Sample Input %d\n",cas++);
        printf("%d\n\n",(res+1)/2); 
    }
    return 0;
}