NKOJ 1781: ISBN Liuhy

2007082602.pas

program ISBN;
uses CRT;
var
   d:array [1..10] of integer;
   i,unk,sumn,ans,t:integer;
   b:boolean; s:string;
begin
   sumn:=0;
   readln(s);
   for i:=1 to 10 do
     begin
       case s[i] of
         '0'..'9':begin b:=true; d[i]:=ord(s[i])-48; end;
         'X':begin b:=true; d[i]:=10; end;
         '?':begin unk:=i; b:=false; end;
       end;
       if b then inc(sumn,(11-i)*d[i]);
     end;
   ans:=-1;
   if unk = 10 then t:=10 else t:=9;
   for i:=0 to t do
     if (sumn+(11-unk)*i) mod 11 = 0 then ans:=i;
   assign(output,'a.txt');
   rewrite(output);
   if ans = 10 then writeln('X') else writeln(ans);
   close(output);
end.