LeetCode:ZigZag Conversion

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".

n=4
P              I              N
A         L  S         I   G
Y   A       H    R
P              I

N=5
P               H
A          S  I
Y      I       R
P   L          I      G
A              N

The key points of this problem is to get the fact that:

• zigSize=2nRows-2
• In each zig, the index of the next element in between (in green) is index + (nRows-i-1)*2. For example, whenRow = 5, the current row=3, index(L) = index(P) + (5-3-1)*2=3+2=5;