Discussion @ 1068. Sum @ Timus Online Judge

Help !!How simple the (1068 Sum) is,but I'm wrong,Why?

Posted by Song Chao (ECUST Mutistar) 9 Feb 2002 07:17

Var N,i,S,Sign:longint;

begin
readln(N);
if N>0 then Sign:=1 else Sign:=-1;
N:=Abs(N);
S:=Sign*(2+N)*(N-1) div 2 ;
writeln(S);
readln;
end.

I'm fool,I misunderstood the problem.

Posted by Song Chao (ECUST Mutistar) 9 Feb 2002 07:44

> Var N,i,S,Sign:longint;
>
> begin
>   readln(N);
>   if N>0 then Sign:=1 else Sign:=-1;
>   N:=Abs(N);
>   S:=Sign*(2+N)*(N-1) div 2 ;
>   writeln(S);
>   readln;
> end.

The Correct Program:

Var N,i,S,Sign:longint;

begin
readln(N);
if N>0 then Sign:=1 else begin N:=-N; Sign:=-1 end;
S:=sign*(1+N)*N div 2;
if sign<0 then S:=S+1;
writeln(S);
readln;
end.

Discussion of Problem 1068. Sum