STPAR - Street Parade

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.


Sample input:
5 1 2 4 3 

Sample output:


The sample input reflects the following situation:

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

hide comments
roisym: 2016-05-07 00:51:11

AC in one go :-) I'm a total beginner and don't have a clue what stacks are and how to use them. I did it by using lists (C#) and careful adding/removing trucks between two lists. Altho this approach seems kinda brute forceish... I now deeply suspect there is a much, much shorter method to check if the trucks can be arranged without actually arranging them (which my current brute program is doing)...

spawngebob: 2016-04-26 01:54:56

So I printed "Yes" instead of "yes". Got WA. Take care of that. It's case sensitive.
Nice test cases given in the comments. Really helped in debugging.

champishere1: 2016-04-09 14:27:02

i am getting a tle ,not able to understand why ,have only used one stack and 2 arrays and is giving correct answers to all the test cases posted in comments?

Dinu Bhai: 2016-03-07 20:38:25

good question of
stack concept for beginners...

vartika: 2016-02-23 12:43:19

i m getting wa ..but showing correct answer in devc

Jamil Siam: 2016-02-14 17:48:03

Awesome problem! :D

avulasaiharish: 2016-02-12 21:40:00

gud one ..!!!

haritha1313: 2016-02-11 09:46:20

nice in one go...thnx for the test cases

mayanksat: 2016-02-07 05:49:19

Want to learn stack? Solve this problem.

amy_96: 2016-01-30 12:08:57

Can't believe i made it :D Beginners should definitely try :)
AC in one go

Added by:Patryk Pomykalski
Time limit:1s-2s
Source limit:50000B
Memory limit:1536MB
Cluster: Cube (Intel G860)
Languages:All except: NODEJS PERL6 VB.NET
Resource:Swiss Olympiad in Informatics 2004