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
srjsunny: 2018-02-06 16:42:14

use strings , size()/(size of column) and reverse() and then see that difference between the indexes will be the column number entered.

abhi007rider: 2018-01-28 18:02:11

Ac in single go !! damnn good!!

rahularity: 2018-01-14 21:14:04

you can do it really fast and the pattern :)

sonuverma: 2018-01-02 15:06:58

my 100th :-)

codesniper99: 2017-12-27 08:57:22


keshavsharma: 2017-12-25 16:05:55

why the hell im getting compilation error here but its running successfully on ideone , wtf so irritating, checked everything, language-option , code, etc etc no shit !!XD

maazalam66: 2017-12-18 13:27:08


Last edit: 2017-12-18 13:48:49
Vaibhav Agnihotri: 2017-09-05 16:33:00

do we need to use 2d arrays?

softxide: 2017-08-08 18:40:34

the question wants you to imagine a 2d array in 1d and apply to and fro motion to it .

prakharvk: 2017-07-22 10:31:32

test cases giving same output but WA on submission

Added by:Adrian Kuegel
Time limit:1s
Source limit:50000B
Memory limit:1536MB
Cluster: Cube (Intel G860)
Resource: ACM East Central North America Regional Programming Contest 2004