hdu 4635 强连通度缩点

思路：想用Tarjan算法进行缩点，并记录每个连通分支的点数。缩点完毕过后，找出所有出度或入度为0的连通分量，假设该连通分量的点数为num[i]，那么

ans=Max(ans,(n-num-1)*(n-num)+(num-1)*num+(n-num)*num-m)；

#include<iostream>
#include<cstring>
#include<cstdio>
#include<algorithm>
#define Maxn 100010
#define Max(a,b) (a)>(b)?(a):(b)
using namespace std;
int head[Maxn],vi[Maxn],dfn[Maxn],low[Maxn],e,lab,top,Stack[Maxn],flag,id[Maxn],in[Maxn],out[Maxn],n,m,Ei[Maxn],num;
__int64 ans;
struct Edge{
    int u,v,next;
}edge[Maxn];
void init()
{
    memset(head,-1,sizeof(head));
    memset(vi,0,sizeof(vi));
    memset(dfn,0,sizeof(dfn));
    memset(low,0,sizeof(low));
    memset(in,0,sizeof(in));
    memset(out,0,sizeof(out));
    memset(Ei,0,sizeof(Ei));
    e=lab=top=flag=num=0;
    ans=0;
}
void add(int u,int v)
{
    edge[e].u=u,edge[e].v=v,edge[e].next=head[u],head[u]=e++;
}
void Tarjan(int u)
{
    dfn[u]=low[u]=++lab;
    vi[u]=1;
    Stack[top++]=u;
    int i,j,v;
    for(i=head[u];i!=-1;i=edge[i].next)
    {
        v=edge[i].v;
        if(!dfn[v])
        {
            Tarjan(v);
            low[u]=min(low[u],low[v]);
        }
        if(vi[v])
            low[u]=min(low[u],dfn[v]);
    }
    if(low[u]==dfn[u])
    {
        ++num;
        int cnt=0;
        do{
            i=Stack[--top];
            vi[i]=0;
            id[i]=num;
            cnt++;
        }while(i!=u);
        Ei[num]=cnt;
        if(n==cnt)
        {
            flag=1;
            return ;
        }
    }
}
int solve()
{
    int i,j;
    for(i=1;i<=n;i++)
    {
        if(!dfn[i])
            Tarjan(i);
        if(flag)
            return 0;
    }
    return 1;
}
int main()
{
    int i,j,a,b,t,Case=0;
    scanf("%d",&t);
    while(t--)
    {
        init();
        scanf("%d%d",&n,&m);
        for(i=1;i<=m;i++)
        {
            scanf("%d%d",&a,&b);
            add(a,b);
        }
        if(!solve()||flag)
        {
            printf("Case %d: -1
",++Case);
            continue;
        }
        for(i=1;i<=n;i++)
            for(j=head[i];j!=-1;j=edge[j].next)
            {
                int u=edge[j].u;
                int v=edge[j].v;
                if(id[u]!=id[v])
                {
                    in[id[v]]++;
                    out[id[u]]++;
                }
            }
        __int64 temp;
        for(i=1;i<=num;i++)
            if(in[i]==0||out[i]==0)
            {
                temp=(__int64)((n-Ei[i])*(n-Ei[i]-1)+Ei[i]*(Ei[i]-1)+(n-Ei[i])*Ei[i]-m);
                ans=Max(ans,temp);
            }
            printf("Case %d: %I64d
",++Case,ans);
    }
    return 0;
}