Zigzag Conversion of String

The string "PAYPALISHIRING" is written in a zigzag pattern on a given number of rows like this: (you may want to display this pattern in a fixed font for better legibility)

P   A   H   N
A P L S I I G
Y   I   R

And then read line by line: "PAHNAPLSIIGYIR"

Write the code that will take a string and make this conversion given a number of rows:

string convert(string text, int nRows);

convert("PAYPALISHIRING", 3) should return "PAHNAPLSIIGYIR".

http://k2code.blogspot.in/2016/03/convert-string-to-zigzag-bottom-up.html
http://n00tc0d3r.blogspot.in/2013/06/zigzag-conversion.html