Discussion @ 1068. Sum @ Timus Online Judge

Ivo There is something very strange about 1068!!! Check this out!!! [5] // Problem 1068. Sum 28 May 2001 00:59

I submitted 1068 twice and I always receive "WA"
Then I read about the formula and I compared the
answers(as you can see down) and they were all
the same. Then I submitted the task once again
with the the formula and I got "AC". Can someone
explain why?

var i,sum1,n,sum:longint;
begin
for n:=-10000 to 10000 do
begin
   {formula}
   if n < 1 then sum := (( 1 + n) * ( 2 - n)) div 2
   else if n >=1 then sum := (( n + 1) * n) div 2;

   {my solution}
   sum1:=0;
   if n=1 then sum1:=1
   else
     if n<=0 then
       for i:=1 downto n do sum1:=sum1+i
     else
       for i:=1 to n do sum1:=sum1+i;

   {if there were different answers}
   if sum<>sum1 then writeln(n,' ',sum1,' ',sum1); readln;
end;

end.

Dinh Quang Hiep (mg9h@yahoo.com) Maybe you got WA with your solution because of your output format [4] // Problem 1068. Sum 28 May 2001 11:50

> I submitted 1068 twice and I always receive "WA"
> Then I read about the formula and I compared the
> answers(as you can see down) and they were all
> the same. Then I submitted the task once again
> with the the formula and I got "AC". Can someone
> explain why?
>
> var i,sum1,n,sum:longint;
> begin
> for n:=-10000 to 10000 do
> begin
>    {formula}
>    if n < 1 then sum := (( 1 + n) * ( 2 - n)) div 2
>    else if n >=1 then sum := (( n + 1) * n) div 2;
>
>    {my solution}
>    sum1:=0;
>    if n=1 then sum1:=1
>    else
>      if n<=0 then
>        for i:=1 downto n do sum1:=sum1+i
>      else
>        for i:=1 to n do sum1:=sum1+i;
>
>    {if there were different answers}
>    if sum<>sum1 then writeln(n,' ',sum1,' ',sum1); readln;
> end;
>
> end.
>

Ivo What do you mean??? [3] // Problem 1068. Sum 29 May 2001 00:07

This is not my output this is a program that compares the
two methods of finding the solution
if sum<>sum1 then writeln(n,' ',sum1,' ',sum1);

Dinh Quang Hiep (mg9h@yahoo.com) i know, but i think your own program have some mistake with the output [2] // Problem 1068. Sum 29 May 2001 10:52

Ivo What mistake??? Tell me more... [1] // Problem 1068. Sum 30 May 2001 00:48

Dinh Quang Hiep (mg9h@yahoo.com) Tong Hop always Vo Dich, and the main reason belongs to ...... // Problem 1068. Sum 30 May 2001 03:04

the main reson belongs to the server. Maybe some thing wrong
with compiling
i've submit your solution

var i,sum1,n,sum:longint;
begin
    read(n);
    {my solution}
    sum1:=0;
    if n=1 then sum1:=1
    else
      if n<=0 then
        for i:=1 downto n do sum1:=sum1+i
      else
        for i:=1 to n do sum1:=sum1+i;

    writeln(sum1);

end.

and got WA, but when i change it to

var i,sum1,n,sum:longint;
begin
    read(n);
    {my solution}
    sum1:=0;
    if n=1 then sum1:=1
    else
      if n<=0 then
            (changing in this line)
        for i:=n to 1 do sum1:=sum1+i

      else
        for i:=1 to n do sum1:=sum1+i;

    writeln(sum1);

end.

And i got AC, i don't know why, but maybe the compiler
define that n is always >=1 and it does not run the command
"for i:=1 downto n", so u get WA. So that, don't use "downto
"when not necessary !

Btw, your program will run slower than any program that use
the simple formula.

QH@

Discussion of Problem 1068. Sum