[BZOJ1023][SHOI2008][仙人掌直径][队列优化DP]cactus仙人掌图

求仙人掌直径裸题
看这篇题解吧
http://z55250825.blog.163.com/blog/static/150230809201412793151890/

#include 
#include 
#include 
#define N 100010

using namespace std;

int n,m,u,v,k,cnt,Ans,tms;
int G[N],dpt[N],f[N],dfn[N],low[N],fa[N],a[N],q[N];
struct edge{
  int t,nx;
}E[20000010];

inline void reaD(int &x){
  char c=getchar(); x=0;
  for(;c>57||c<48;c=getchar());for(;c>=48&&c<=57;x=x*10+c-48,c=getchar());
}

inline void Insert(int x,int y){
  E[++cnt].t=y; E[cnt].nx=G[x]; G[x]=cnt;
  E[++cnt].t=x; E[cnt].nx=G[y]; G[y]=cnt;
}

inline void dp(int x,int y){
  int deep=dpt[y]-dpt[x]+1;
  for(int i=y;i!=x;i=fa[i]) a[deep--]=f[i]; a[deep]=f[x];
  deep=dpt[y]-dpt[x]+1;
  for(int i=1;i<=deep;i++) a[i+deep]=a[i];
  int l=1,r=0;
  for(int i=1;i<=2*deep;i++){
    while(l<=r&&i-q[l]>deep/2) l++;
    if(l<=r) Ans=max(Ans,a[i]+i+a[q[l]]-q[l]);
    while(l<=r&&a[q[r]]-q[r]<=a[i]-i) r--;
    q[++r]=i;
  }
  for(int i=2;i<=deep;i++) f[x]=max(f[x],a[i]+min(i-1,deep-i+1));
}

void dfs(int x,int p){
  dfn[x]=low[x]=++tms;
  dpt[x]=dpt[p]+1; fa[x]=p;
  for(int i=G[x];i;i=E[i].nx)
    if(E[i].t!=p){
      if(!dfn[E[i].t]) dfs(E[i].t,x);
      low[x]=min(low[x],low[E[i].t]);
      if(low[E[i].t]>dfn[x]){
    Ans=max(Ans,f[x]+f[E[i].t]+1);
    f[x]=max(f[x],f[E[i].t]+1);
      }
    }
  for(int i=G[x];i;i=E[i].nx)
    if(x!=fa[E[i].t]&&dfn[x]x,E[i].t);
}

int main(){
  freopen("1.in","r",stdin);
  freopen("1.out","w",stdout);
  reaD(n); reaD(m);
  for(int i=1;i<=m;i++){
    reaD(k); reaD(u);
    for(int j=2;j<=k;j++)
      reaD(v),Insert(u,v),u=v;
  }
  dfs(1,0);
  printf("%d\n",Ans);
}