bzoj1211

prufer码水题
（n-2)！/[(d1-1)!*(d2-1)!*…*(dn-1)!]

 var c:array[..] of longint;
     x,n,i,j,s:longint;
     ans:int64;

 begin
   readln(n);
   if n= then
   begin
     readln(x);
     if x= then writeln()
     else writeln();
     halt;
   end;
   for i:= to n do
   begin
     read(x);
     if (x<) or (x>n) then
     begin
       writeln();
       halt;
     end;
     for j:= to x- do
       inc(c[j]);
     s:=s+x-;
   end;
   if s<>n- then
   begin
     writeln();
     halt;
   end;
   ans:=;
   for i:= to n- do
   begin
     ans:=ans*int64(i);
     for j:= to n do
     begin
       while (c[j]>) and (ans mod j=) do
       begin
         dec(c[j]);
         ans:=ans div j;
       end;
     end;
   end;
   writeln(ans);
 end.