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
ferdinant_2012: 2024-03-27 13:01:58

[Simes]: with nearly 18000 users ACed, I don't think anybody needs this framework

Last edit: 2024-03-27 14:49:41
uditmehra_827: 2023-11-01 14:27:55

That was good question... it took me hour..

shashank_lol: 2023-04-11 10:05:07

Thanks @harsh_arora

drago_codes: 2022-12-09 03:36:13

Simple problem, can be easily solved using 1 stack

trieutruong_3k: 2022-08-08 19:38:11

Be careful your input. There are several testcases as input, the input ends only when it meets '0'.

old_monk1: 2022-07-29 12:30:19

Omg! what a problem. Never knew ad hoc could be so interesting.

hp_777: 2022-05-24 10:17:07

Thanks @harsh_arora I was taking t as input for test cases rather than n directly.

sarkybastard: 2022-02-10 20:37:18

@rz_ai you could write that same comment against every single problem

rz_ai: 2022-02-09 16:10:34

remember to clear the stack,array,counter for each iteration

j_kumar221: 2022-01-20 14:43:36

Be carefull for newline and case "Yes' and 'yes' are different.

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