Strongly connected---hdu4635（强联通分量）

#include<stdio.h>
#include<string.h>
#include<vector>
#include<algorithm>
#define N 100005
#define INF 0xfffffff
using namespace std;

int head[N], cnt;
int top, Is[N], Stack[N], low[N], dfn[N], Time, n, m;
int nBlock, Block[N];
int Cnt[N], Out[N], In[N];
struct Edge
{
    int v, next;
}e[N];
void Init()
{
    Time = cnt = top = nBlock = 0;
    memset(Cnt, 0, sizeof(Cnt));
    memset(low, 0, sizeof(low));
    memset(dfn, 0, sizeof(dfn));
    memset(Stack,0 , sizeof(Stack));
    memset(Is, 0, sizeof(Is));
    memset(Out, 0, sizeof(Out));
    memset(In, 0, sizeof(In));
    memset(Block, 0, sizeof(Block));
    memset(head, -1, sizeof(head));
}
void Add(int u, int v)
{
    e[cnt].v = v;
    e[cnt].next = head[u];
    head[u] = cnt++;
}
void Tajar(int u, int father)
{
    Stack[top++]=u;
    low[u] = dfn[u] = ++Time;
    Is[u] = 1;
    int v;
    for(int i=head[u]; i!=-1; i=e[i].next)
    {
        v = e[i].v;
        if(!dfn[v])
        {
            Tajar(v, u);
            low[u] = min(low[u], low[v]);
        }
        else if(Is[v])
            low[u] = min(low[u], dfn[v]);
    }
    if(low[u]==dfn[u])
    {
        ++nBlock;
        do
        {
            v=Stack[--top];
            Is[v] = 0;
            Block[v] = nBlock;
            Cnt[nBlock]++;
        }while(u!=v);
    }
}

int main()
{
    int T, t=1, x, y;
    scanf("%d", &T);
    while(T--)
    {
        Init();
        scanf("%d%d", &n, &m);
        for(int i=1; i<=m; i++)
        {
            scanf("%d%d", &x, &y);
            Add(x, y);
        }
        for(int i=1; i<=n; i++)
        {
            if(!low[i])
                Tajar(i, -1);
        }
        for(int i=1; i<=n; i++)
        {
            for(int j=head[i]; j!=-1; j=e[j].next)
            {
                int u = Block[i];
                int v = Block[e[j].v];
                if(u != v)
                {
                    Out[v]++;
                    In[u]++;
                }
            }
        }
        y = INF;
        for(int i=1; i<=nBlock; i++)
        {
            if(!In[i] || !Out[i])
                y=min(y, Cnt[i]);
        }
        x = n - y;
        long long ans=(long long)n*(n-1)-x*y-m;
        if(nBlock==1)
            printf("Case %d: -1\n", t++);
        else
            printf("Case %d: %lld\n", t++, ans);
    }
    return 0;
}