[BZOJ3779]重组病毒(LCT+DFS序线段树)

同[BZOJ4817]树点涂色，只是多了换根操作，分类讨论下即可。

 #include<cstdio>
 #include<algorithm>
 #define lc ch[x][0]
 #define rc ch[x][1]
 #define ls (x<<1)
 #define rs (ls|1)
 #define lson ls,L,mid
 #define rson rs,mid+1,R
 #define rep(i,l,r) for (int i=(l); i<=(r); i++)
 #define For(i,x) for (int i=h[x],k; i; i=nxt[i])
 typedef long long ll;
 using namespace std;

 const int N=;
 char op[];
 ll tag[N<<],sm[N<<];
 int n,m,u,v,x,rt,cnt,tim,rev[N],h[N],nxt[N<<],to[N<<];
 int L[N],R[N],dep[N],fa[N][],ch[N][],sz[N],f[N];
 void add(int u,int v){ to[++cnt]=v; nxt[cnt]=h[u]; h[u]=cnt; }

 inline int rd(){
     int x=; char ch=getchar(); bool f=;
     while (ch<'' || ch>'') f|=ch=='-',ch=getchar();
     while (ch>='' && ch<='') x=(x<<)+(x<<)+(ch^),ch=getchar();
     return f ? -x : x;
 }

 int jump(int x,int k){
     for (int i=; ~i; i--) if (k&(<<i)) x=fa[x][i]; return x;
 }

 void push(int x,int L,int R){
     if (!tag[x]) return;
     int mid=(L+R)>>;
     sm[ls]+=tag[x]*(mid-L+); tag[ls]+=tag[x];
     sm[rs]+=tag[x]*(R-mid); tag[rs]+=tag[x];
     tag[x]=;
 }

 void mdf(int x,int L,int R,int l,int r,int k){
     if (L==l && r==R){ sm[x]+=1ll*k*(R-L+); tag[x]+=k; return; }
     int mid=(L+R)>>; push(x,L,R);
     if (r<=mid) mdf(lson,l,r,k);
     else if (l>mid) mdf(rson,l,r,k);
         else mdf(lson,l,mid,k),mdf(rson,mid+,r,k);
     sm[x]=sm[ls]+sm[rs];
 }

 ll que(int x,int L,int R,int l,int r){
     if (L==l && r==R) return sm[x];
     int mid=(L+R)>>; push(x,L,R);
     if (r<=mid) return que(lson,l,r);
     else if (l>mid) return que(rson,l,r);
         else return que(lson,l,mid)+que(rson,mid+,r);
 }

 void dfs(int x){
     L[x]=++tim; dep[x]=dep[fa[x][]]+; sz[x]=;
     rep(i,,) fa[x][i]=fa[fa[x][i-]][i-];
     mdf(,,n,L[x],L[x],dep[x]);
     For(i,x) if ((k=to[i])!=fa[x][]) fa[k][]=x,f[k]=x,dfs(k),sz[x]+=sz[k];
     R[x]=tim;
 }

 bool isrt(int x){ return (!f[x]) || (ch[f[x]][]!=x && ch[f[x]][]!=x); }
 void put(int x){ swap(lc,rc); rev[x]^=; }
 void push(int x){ if (rev[x]) put(lc),put(rc),rev[x]=; }
 void pd(int x){ if (!isrt(x)) pd(f[x]); push(x); }

 void rot(int x){
     int y=f[x],z=f[y],w=ch[y][]==x;
     if (!isrt(y)) ch[z][ch[z][]==y]=x;
     f[x]=z; f[y]=x; f[ch[x][w^]]=y;
     ch[y][w]=ch[x][w^]; ch[x][w^]=y;
 }

 void splay(int x){
     pd(x);
     while (!isrt(x)){
         int y=f[x],z=f[y];
         if (!isrt(y)) (ch[z][]==y)^(ch[y][]==x) ? rot(x) : rot(y);
         rot(x);
     }
 }

 void work(int x,int k){
     if (rt==x) mdf(,,n,,n,k);
     else if (L[rt]>=L[x] && L[rt]<=R[x]){
         int t=jump(rt,dep[rt]-dep[x]-);
         if (L[t]>) mdf(,,n,,L[t]-,k);
         if (R[t]<n) mdf(,,n,R[t]+,n,k);
     }else mdf(,,n,L[x],R[x],k);
 }

 int find(int x){
     push(x);
     while (lc) x=lc,push(x);
     return x;
 }

 void access(int x){
     for (int y=; x; y=x,x=f[x]){
         splay(x);
         if (rc) work(find(rc),);
         if (y) work(find(y),-);
         rc=y;
     }
 }

 void mkrt(int x){ access(x); splay(x); put(x); }

 int main(){
     freopen("bzoj3779.in","r",stdin);
     freopen("bzoj3779.out","w",stdout);
     n=rd(); m=rd();
     rep(i,,n) u=rd(),v=rd(),add(u,v),add(v,u);
     dfs(); rt=;
     while (m--){
         scanf("%s",op); x=rd();
         if (op[]=='L') access(x);
         if (op[]=='C') mkrt(x),rt=x;
         if (op[]=='Q'){
             if (rt==x) printf("%.10lf\n",.*que(,,n,,n)/n);
             else if (L[rt]>=L[x] && L[rt]<=R[x]){
                 int t=jump(rt,dep[rt]-dep[x]-);
                 ll res1=L[t]> ? que(,,n,,L[t]-) : ;
                 ll res2=R[t]<n ? que(,,n,R[t]+,n) : ;
                 printf("%.10lf\n",.*(res1+res2)/(n-sz[t]));
             }else printf("%.10lf\n",.*que(,,n,L[x],R[x])/sz[x]);
         }
     }
     return ;
 }