TOANDFRO - To and Fro

Mo and Larry have devised a way of encrypting messages. They first decide secretly on the number of columns and write the message (letters only) down the columns, padding with extra random letters so as to make a rectangular array of letters. For example, if the message is “There’s no place like home on a snowy night” and there are five columns, Mo would write down

t o i o y
h p k n n
e l e a i
r a h s g
e c o n h
s e m o t
n l e w x

Note that Mo includes only letters and writes them all in lower case. In this example, Mo used the character ‘x’ to pad the message out to make a rectangle, although he could have used any letter. Mo then sends the message to Larry by writing the letters in each row, alternating left-to-right and right-to-left. So, the above would be encrypted as


Your job is to recover for Larry the original message (along with any extra padding letters) from the encrypted one.


There will be multiple input sets. Input for each set will consist of two lines. The first line will contain an integer in the range 2...20 indicating the number of columns used. The next line is a string of up to 200 lower case letters. The last input set is followed by a line containing a single 0, indicating end of input.


Each input set should generate one line of output, giving the original plaintext message, with no spaces.






hide comments
vivekrnj: 2016-03-10 19:49:57

a simple one...just to look on pattern....Got ac in 1 go

giriprasad kemburu: 2016-03-07 07:21:48

@mtrworld Thank you!!!!!!!!!

shyam55555: 2016-02-02 10:56:30

@mtrworld Thank You!

try2catch: 2016-01-19 12:22:04

Wanna play with loops? - this question is for you......

saurabh_1999: 2016-01-15 14:27:36

AC in one go :)

surbhi_ag1: 2016-01-15 13:10:48

@deepak garg it doesn't matter. The receiver has to understand the message and has to figure it out along with the padding letters.

arjun: 2015-12-27 10:25:29

0 1 2
5 4 3
6 7 8
11 10 9

Just observe the pattern.
No need to use any String Library Functions.
Simple with Basic Maths.

ov3rk1ll: 2015-12-27 09:39:07

@mtrworld can you explain why???

mtrworld: 2015-10-28 10:43:50

If anyone submitting the solution in java. please append a blank line/SOP statement before you take in next input. Else it will throw wrong answer while submitting the solution.

sarthak_8: 2015-10-18 16:09:58

It shows WA in spoj but the answer I get on Ideone is correct. Can anybody please help me with this code

Added by:Adrian Kuegel
Time limit:0.959s
Source limit:50000B
Memory limit:1536MB
Cluster: Cube (Intel G860)
Resource: ACM East Central North America Regional Programming Contest 2004