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S_PARADE - Street parade (challenge)

For sure, the love mobiles will roll again on this summer's street parade. Each year, the organisers decide on a fixed order for the decorated trucks. Experience taught them to keep free a side street to be able to bring the trucks into order.

The side street is so narrow that no two cars can pass each other. Thus, the love mobile that enters the side street last must necessarily leave the side street first. Because the trucks and the ravers move up closely, a truck cannot drive back and re-enter the side street or the approach street.

You are given the order in which the love mobiles arrive. Write a program that decides if the love mobiles can be brought into the order that the organisers want them to be.


There are several test cases. The first line of each test case contains a single number n, the number of love mobiles. The second line contains the numbers 1 to n in an arbitrary order. All the numbers are separated by single spaces. These numbers indicate the order in which the trucks arrive in the approach street. No more than 1000 love mobiles participate in the street parade.

Input ends with number 0.


For each test case your program has to output a line containing a single word yes if the love mobiles can be re-ordered with the help of the side street, and a single word no in the opposite case.


5 1 2 4 3



The sample input reflects the following situation:

The five trucks can be re-ordered in the following way:

Special thanks to Patryk Pomykalski for tests to this task.

Added by:Piotr Kąkol
Time limit:8.069s
Source limit:50000B
Memory limit:1536MB
Cluster: Cube (Intel G860)
Languages:All except: SCM qobi
Resource:Copy of task STPAR with different scoring

hide comments
2014-06-27 21:32:47 Mitch Schwartz
@Piotr: There seems to be an empty line at the end of input for at least one input file. I'd consider that a mistake. If we are supposed to treat it as a permutation of the empty set, then we should print "yes" for that line instead of ignoring it. And there is no mention of it in the problem statement.

Edit: Thanks for the update and rejudge :)

Last edit: 2014-09-14 03:02:41
2012-03-22 03:06:32 Piotr KÄ…kol
I've just done a rejudge. So now some AC may got WA. Please contact me for tests in which You have WA. Sorry for the last rejudge. I didn't have time to ix it till now.
2012-03-21 19:24:08 Jander
What's broken / changed ?
2011-03-11 23:27:41 Piotr KÄ…kol
Yes of course. :-)
Fixed. Thank You for letting me know. I'll check if there are more suh tasks.
Edit: No, it was the only one.

Last edit: 2011-03-11 23:35:19
2011-03-10 12:12:14 Hallvard Norheim Bø
Is it possible to add Python 3.1.2 to list of allowed languages?
2010-04-04 21:50:50 Piotr KÄ…kol
Now everything is fine.
Sorry for impediments.
2010-04-04 21:26:08 numerix
Yes, there seems something wrong with the data. I submitted my AC Code from SPOJ No. 95 (STPAR) and get RTE here.
2010-04-04 18:30:51 HWK
I get REs. When I catch the errors for the input of all odd lines (i.e. the number of love mobiles) then there are no more REs but I get WA. So it seems that the format of the input-file isn't like the description.
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