bzoj 1023: [SHOI2008]cactus仙人掌图 tarjan索环&&环上单调队列

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<queue>
#include<set>
using namespace std;
#define PROB "cactus"
#define MAXN 100010
#define MAXV MAXN
#define MAXE MAXV * 2
#define INF 0x3f3f3f3f
struct edge
{
        int x,y,id;
}e[MAXE];
int n,m;
int prv[MAXN];
struct Edge
{
        int sp,np,val,id;
        Edge *next;
}E[MAXE],*V[MAXV];
int tope;
int dfn[MAXN],dfstime=0;
int ans=0;
void addedge(int x,int y,int id,int z=1)
{
        E[++tope].np=y;
        E[tope].id=id;
        E[tope].sp=x;
        E[tope].val=z;
        E[tope].next=V[x];
        V[x]=&E[tope];
}
int len[MAXN];
int arr[MAXN];
int seq[MAXN];
int vis[MAXN];
void solve(int rt,int now)
{
        int tota=0;
        int x,i;
        x=now;
        while (x!=rt)
        {
                arr[tota++]=len[x];
                x=prv[x];
        }
        arr[tota++]=0;
        for (i=0;i<tota;i++)
                arr[i+tota]=arr[i];
        x=0;
        seq[0]=0;
        int tail=0,head=0;
        for (i=1;i<tota*2;i++)
        {
                while (i-seq[head]>tota/2)head++;
                ans=max(ans,arr[seq[head]]+(i-seq[head])+arr[i]);
                while (tail>=head && arr[seq[tail]] + (i-seq[tail]) <=arr[i])tail--;
                seq[++tail]=i;
        }
}
int low[MAXN];
bool inc[MAXN];
vector<int> ptr[MAXN];
void dfs(int now,int pnt=-1)
{
        low[now]=dfn[now]=++dfstime;
        Edge *ne;
        vis[now]=1;
        int x=-1,y=-1;
        int st=-1,rt;
        for (ne=V[now];ne;ne=ne->next)
        {
                if (ne->np==prv[now])continue;
                if (vis[ne->np]==1)
                {
                        ptr[ne->np].push_back(now);
                        low[now]=min(low[now],dfn[ne->np]);
                }else if (!vis[ne->np])
                {
                        prv[ne->np]=now;
                        dfs(ne->np,now);
                        low[now]=min(low[now],low[ne->np]);
                }
        }
        for (int i=0;i<ptr[now].size();i++)
        {
                st=ptr[now][i],rt=now;
                int sizc=1;
                x=st;
                inc[x]=true;
                while (x!=rt)
                {
                        x=prv[x];
                        inc[x]=true;
                        sizc++;
                }
                x=st;
                int d=1;
                int t=0;
                while (x!=rt)
                {
                        t=max(t,min(d,sizc-d)+len[x]);
                        d++;
                        x=prv[x];
                }
                ans=max(ans,t+len[rt]);
                len[rt]=max(len[rt],t);
                solve(rt,st);
        }
        x=y=0;
        if (!inc[now])
        {
                for (ne=V[now];ne;ne=ne->next)
                {
                        if (dfn[ne->np]<dfn[now])continue;
                        if (y<len[ne->np]+1)
                        {
                                y=len[ne->np]+1;
                                if (x<y)swap(x,y);
                        }
                }
        }
        if (low[now]==dfn[now])
        {
                if (prv[now])ans=max(ans,len[now]+1+len[prv[now]]);
                if (prv[now])len[prv[now]]=max(len[prv[now]],len[now]+1);
        }
        ans=max(ans,x+y);
        vis[now]=2;
}
int deg[MAXN];
void work()
{
        int i,x,y;
        for (i=0;i<m;i++)
        {
                x=e[i].x;
                y=e[i].y;
                addedge(x,y,i);
                addedge(y,x,i);
                deg[x]++;
                deg[y]++;
        }
        int core=0;
        for (i=1;i<=n;i++)
        {
                if (deg[i]==1)core=i;
                if (!core && deg[i]%2==1)core=i;
        }
        if (!core)core=1;
        dfs(core,core);
}
set<pair<int,int> > S;
int main()
{
        //freopen(PROB".in","r",stdin);
        //freopen(PROB".out","w",stdout);
        int l;
        scanf("%d%d",&n,&l);
        int i,j,k;
        int x,y,z;
        for (i=0;i<l;i++)
        {
                scanf("%d",&x);
                scanf("%d",&y);
                for (j=1;j<x;j++)
                {
                        scanf("%d",&z);
                        e[m].x=y;
                        e[m].y=z;
                        m++;
                        y=z;
                }
        }
        for (i=0;i<m;i++)
        {
                if (e[i].x>e[i].y)swap(e[i].x,e[i].y);
                if (e[i].x==e[i].y || S.find(make_pair(e[i].x,e[i].y))!=S.end())
                {
                        i--;m--;
                        continue;
                }else
                {
                        S.insert(make_pair(e[i].x,e[i].y));
                }
                e[i].id=i;
        }
        work();
        printf("%d\n",ans);
}