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Equivalent Sets

4 0
3 2
1 2
1 3

4
2
Hint
Case 2: First prove set 2 is a subset of set 1 and then prove set 3 is a subset of set 1.
 

#include"stdio.h"
#include"string.h"
#include"queue"
#include"vector"
#include"algorithm"
using namespace std;
#define N 20005
#define M 50005
#define min(a,b) (a<b?a:b)
const int inf=1000000;
struct node
{
    int u,v,next;
}e[M];
int t,bcnt,index,stop,ans;
int head[N],dfn[N],low[N],stap[N],mark[N],be[N];
int indeg[N],out[N];
void add(int u,int v)
{
    e[t].u=u;
    e[t].v=v;
    e[t].next=head[u];
    head[u]=t++;
}
void tarjan(int u)
{
    int i,v;
    dfn[u]=low[u]=++index;
    stap[++stop]=u;
    mark[u]=1;
    for(i=head[u];i!=-1;i=e[i].next)
    {
        v=e[i].v;
        if(!dfn[v])
        {
            tarjan(v);
            low[u]=min(low[u],low[v]);
        }
        else if(mark[v])
            low[u]=min(low[u],dfn[v]);
    }
    if(low[u]==dfn[u])
    {
        bcnt++;
        do
        {
            v=stap[stop--];
            mark[v]=0;
            be[v]=bcnt;
        }
        while(u!=v);
        ans++;
    }
}
void solve(int n)
{
    int i;
    memset(dfn,0,sizeof(dfn));
    index=stop=bcnt=0;
    for(i=1;i<=n;i++)
    {
        if(!dfn[i])
            tarjan(i);
    }
}
void work(int n)
{
    int i,j,u,v,t1,t2;
    memset(indeg,0,sizeof(indeg));
    memset(out,0,sizeof(out));
    for(i=1;i<=n;i++)
    {
        u=be[i];
        for(j=head[i];j!=-1;j=e[j].next)
        {
            v=be[e[j].v];
            if(u!=v)
            {
                indeg[v]++;
                out[u]++;
            }
        }
    }
    t1=t2=0;
    for(i=1;i<=bcnt;i++)
    {
        if(indeg[i]==0)
            t1++;
        if(out[i]==0)
            t2++;
    }
    printf("%d\n",t1>t2?t1:t2);
}
int main()
{
    int n,m,u,v;
    while(scanf("%d%d",&n,&m)!=-1)
    {
        t=0;
        memset(head,-1,sizeof(head));
        while(m--)
        {
            scanf("%d%d",&u,&v);
            add(u,v);
        }
        ans=0;
        solve(n);
       // printf("%d\n",ans);
        if(ans==1)
            printf("0\n");
        else
            work(n);
    }
    return 0;
}

hdu 3836 Equivalent Sets（强连通分量--加边）,布布扣,bubuko.com

hdu 3836 Equivalent Sets（强连通分量--加边）

标签：des   style   color   java   os   io   strong   for   

原文地址：http://blog.csdn.net/u011721440/article/details/38490781