UKROBOT - Editorial

editorial
, , , , ,
5

What will happen if the bot finds an obstacle, whether it will stop there forever or move again if it finds some instructions which satisfy it’s moving rule?

6

If it has an instruction which will move it into the obstacle, it ignores it, meaning it may do other instructions that don’t force it into the obstacle.

1 Like
8

I don’t get this part …

In the problem statement, it’s stated that :

When performing an instruction, if the cell it needs to move to is free, then it moves to that cell; otherwise, it stays in its current cell.

So, if the robot is sent to the square with the obstacle, it should stop, right ?
So, why visiting all the possible cells minus 1 is not enough to know the obstacle position ?

3 Likes
9

nevermind … I see the issue now …

1 Like
10

I have a little confusion about dircetions.

for subtask 1.

L: move one cell to the left, i.e. from a cell (x,y) to (x−1,y)
R: move one cell to the right, i.e. from a cell (x,y) to (x+1,y)
D: move one cell down, i.e. from a cell (x,y) to (x,y−1)
U: move one cell up, i.e. from a cell (x,y) to (x,y+1)

then U + 20*R will generate sequence like this (00 01 11 21 31 41 51) then how can x be
1<=X<=R (row) ?

1 Like
11

According to given problem statement, 1<=x<=r && 1<=y<=c ;
According to editorial, 1<=x<=c && 1<=y<=r ;
I think they are different.

1 Like
12

I am having a feeling that either the question was not well written , or my English is bad as even after 2-3 readings I was unable to understand the problem…

17 Likes
13

The question says X<=R and Y<=C. You have taken the reverse here. Am i missing anything or is there a misprint in the question?

1 Like
14

Yeah. Terminology was a bit confusing. R is the number of “rows” - y-positions, and C is the number of “columns” - x-positions.

edit: I think this is wrong

1 Like
15

Yes,It is wrong not only in editorial but testing too.
when I reversed the r and c in my solution my solution got AC.

1 Like
16

This line should have been added in the question. Most people interpreted that the robot would just stay immobile after encountering an obstacle. Anyways good problem.

1 Like
17

There was an announcement regarding the same in the middle of the contest.
I missed the change too :confused:

18

Statement of UKROBOT had 1 <= X <= C, 1 <= Y <= R, instead of 1 <= X <= R, 1 <= Y <= C, it is fixed now.

this is from announcements.

So I think question was correct but after announcement it got wrong.

1 Like
19

Yeah… I have considered it will be immobile after it find an obstacle, That’s why I was not able to figure out why I am getting WA

21

Shit! I misunderstood this problem

1 Like
22

Exactly!

23

Okay, to be honest, that announcement is actually tripping me up. Sorry that it ended up so confusing, we probably should have just made it rows/columns instead of Cartesian coordinates.

3 Likes
24

Hey man! Don’t worry. You are good.

25

That’s not an issue. It’s okay.
Question quality is what matters which was quite good.

26

i really wonder how the tester tests these kind of problems