bz上为数不多的模板题，致敬一下

代码长度应该可以缩短，就不多说了，贴一个先

var i,j,k,l,m,n,p,q,t,tt:longint;     key,s,left,right:array[0..100005] of longint;       procedure lro(var t:longint); var k:longint; begin    k:=right[t];     right[t]:=left[k];     left[k]:=t;     s[k]:=s[t];     s[t]:=s[left[t]]+s[right[t]]+1;     t:=k; end;       procedure rro(var t:longint); var k:longint; begin    k:=left[t];     left[t]:=right[k];     right[k]:=t;     s[k]:=s[t];     s[t]:=s[left[t]]+s[right[t]]+1;     t:=k; end;   procedure maintain(var t:longint;flag:boolean); begin    if not flag then    begin        if s[left[left[t]]]>s[right[t]] then rro(t)             else if s[right[left[t]]]>s[right[t]] then            begin                lro(left[t]);                 rro(t);             end else exit;     end else     begin        if s[right[right[t]]]>s[left[t]] then lro(t)             else if s[left[right[t]]]>s[left[t]] then             begin                rro(right[t]);                 lro(t);             end else exit;     end;     maintain(left[t],false);     maintain(right[t],true);     maintain(t,false);     maintain(t,true); end;       procedure insert(var t:longint;v:longint); begin    if t=0 then    begin        inc(tt);         t:=tt;         s[t]:=1;         key[t]:=v;     end else    begin        inc(s[t]);         if v
     
      =key[t]);     end; end;   function delete(var t:longint;v:longint):longint; begin    dec(s[t]);     if (v=key[t])or(v
      
       key[t])and(right[t]=0) then    begin        delete:=key[t];         if (left[t]=0)or(right[t]=0) then t:=left[t]+right[t] else key[t]:=delete(left[t],key[t]+1);     end else if v
       
        v then exit(select(left[t],v))         else exit(select(right[t],v-s[left[t]]-1)); end;   function pred(t,v:longint):longint; begin    if t=0 then exit(-1);     if key[t]>=v then exit(pred(left[t],v))         else begin            pred:=pred(right[t],v);             if pred=-1 then exit(key[t]);         end; end;   function succ(t,v:longint):longint; begin    if t=0 then exit(-1);     if key[t]<=v then exit(succ(right[t],v))         else begin            succ:=succ(left[t],v);             if succ=-1 then exit(key[t]);         end; end;   begin    readln(n);     for i:=1 to n do     begin        readln(p,q);         case p of             1:insert(t,q);             2:delete(t,q);             3:writeln(rank(t,q));             4:writeln(select(t,q));             5:writeln(pred(t,q));             6:writeln(succ(t,q));         end;     end; end.