UVA 10972 RevolC FaeLoN(邊雙聯通+縮點)

#include<iostream>
#include<vector>
#include<cstring>
using namespace std;
const int maxn=1000+5;
const int maxm=maxn*maxn;
struct Edge{
    int u,v;
    Edge(int u=0,int v=0):u(u),v(v){}
}e[maxm];
int n,m,tot,stamp,dfn[maxn],low[maxn],bccno[maxn],bcc_cnt,de[maxn];
vector<int> vec[maxn],bcc[maxn];
bool g[maxn][maxn],isbridge[maxm];

void tarjan(int index,int fa)
{
    int tmp;
    dfn[index]=low[index]=++stamp;
    for(int i=0;i<vec[index].size();i++)
    {
        tmp=e[vec[index][i]].v;
        if(!dfn[tmp])
        {
            tarjan(tmp,index);
            low[index]=min(low[index],low[tmp]);
            if(low[tmp]>dfn[index])
                isbridge[vec[index][i]]=isbridge[vec[index][i]^1]=1;
        }
        else if(dfn[tmp]<dfn[index] && tmp!=fa)
        {
            low[index]=min(low[index], dfn[tmp]);
        }
    }
}

void dfs(int index)
{
    dfn[index]=1;
    bccno[index]=bcc_cnt;
    for(int i=0;i<vec[index].size();i++)
    {
        int tmp=vec[index][i];
        if(isbridge[tmp])
            continue;
        if(!dfn[e[tmp].v])
        {
            dfs(e[tmp].v);
        }
    }
}

void find_ebcc(){
    bcc_cnt=stamp=0;
    memset(dfn,0,sizeof(dfn));
    memset(low,0,sizeof(low));
    memset(isbridge,0,sizeof(isbridge));
    memset(bccno,0,sizeof(bccno));
    memset(bcc,0,sizeof(bcc));
    for(int i=1;i<=n;i++)
        if(!dfn[i])
            tarjan(i, -1);
    memset(dfn,0,sizeof(dfn));
    for(int i=1;i<=n;i++)
    {
        if(!dfn[i])
        {
            bcc_cnt++;
            dfs(i);
        }
    }               
}

void addedge(int u,int v)
{
    e[tot]=Edge(u,v);
    vec[u].push_back(tot++);
}
int main()
{
    while(~scanf("%d%d",&n,&m))
    {
        tot=0;
        memset(vec,0,sizeof(vec));
        for(int i=0;i<m;i++){
            int u,v;
            scanf("%d%d",&u,&v);
            addedge(u,v);
            addedge(v,u);
        }
        find_ebcc();
        memset(de,0,sizeof(de));
        for(int i=0;i<tot;i++){
            if(bccno[e[i].u]!=bccno[e[i].v]) {de[bccno[e[i].u]]++;}
        }
        int ans=0;
        for(int i=1;i<=bcc_cnt;i++){
            if(de[i]==1) ans++;
            if(de[i]==0) ans+=2;
        }
        if(bcc_cnt==1) printf("0\n");
        else printf("%d\n",(ans+1)/2);
    }
    return 0;
}