10730 - Antiarithmetic?

[Destination Goa]

It was wrong, I've just checked

I checked that 0,1,2,3...n-1 alter directions, then that 0,2,4,6,... alter directions, then that 0,3,6,9,... alter directions and so on. However, sub-sequences like 1,3,5 wouldn't be tested and that killed the method with smallest counter-example of 6 items. Fortunately (or not) it wasn't in test data. It is: 0 4 2 1 3 5. If we check same way from the higher end, than smallest counter-example consists of 7 items.

My head was too full with number of inverses by the time I developed that wrong algorithm. I am sorry

[james299]

Hi!
The problem statement says

For example, the sequence (2, 0, 1, 4, 3) is an antiarithmetic permutation of 5. The sequence (0, 5, 4, 3, 1, 2) is not an antiarithmetic permutation as its first, fifth and sixth term (0, 1, 2) form an arithmetic progression; and so do its second, forth and fifth term (5, 3, 1).

So, it seems to be ok with decreasing order sequence.
And I mutiply by -1 when the difference is negative.

Code: Select all

If Third = 5 - 3 - 3 ; (< 0)
   Third *= -1;
 if(Third<n&&Y[Third]>j) ...

But I got WA.And I try to get rid of decreasing order sequence as Misof said, it got AC.

Thanks for your precious time.

[marif]

Anyone please post some critical inputs and outputs on this topic. It will be very helpful.

[Tanu]

what is the wrong with my code...
I save the indexes and checked for n, is the position if n+1 and n+2 is greater than position of n...
is there anything wrong understanding with my code...
plz help...

Code: Select all

#include<stdio.h>
#include<string.h>
long in[10005],pos[10005];
main()
{
	char s[15];
	long len,n,i;
	bool flag;
	while(1)
	{
		scanf("%s",s);
		if(strcmp(s,"0")==0)
			break;
		len = strlen(s);
		n = 0;
		for(i=0;i<len;i++)
			if(s[i]>='0' && s[i]<='9')
				n = n*10+(s[i]-'0');
		for(i=1;i<=n;i++)
		{
			scanf("%ld",&in[i]);
			pos[in[i]] = i;
		}
		flag = false;
		for(i=1;i<=n-2;i++)
			if(i<pos[in[i]+1] && pos[in[i]+1] < pos[in[i]+2])
			{
				flag = true;;
				break;
			}
		if(flag)
			printf("no\n");
		else
			printf("yes\n");
	}
	return 0;
}

Thinking you are a kind helper...
...Tanu[/list]

[Darko]

Now you didn't even check 3 posts above yours...

For 0 4 2 1 3 5 your program gives "yes".

[morkoh]

Why is it enough to check only rising arithmetic sequences?
My code passes the judge, but it outputs a wrong answer for
5: 0 4 3 2 1 --> "yes"
5: 2 4 3 1 0 --> "yes"
when both should be "no", first one has (4,3,2,1) second (2,1,0).

The code which checks both rising and falling arithmetic sequences also gets accepted.
A bit weird, I guess.

[brianfry713]

That would imply that the judge's I/O is weak if your incorrect code gets AC.