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".

这道题目就是一个找规律的题目，没有其他的方法，题目已经给出nRows = 3的情况，我们可以再写出nRows = 4时的情况。代码如下：

public class Solution {
    public String convert(String s, int numRows) {
        if(numRows == 1) return s;
        StringBuilder sb = new StringBuilder();
        int next = 2 * numRows - 2;
        int mod = 0;
        while(mod < numRows) {
            for(int i = 0; i < s.length(); i++) {
                if(i % next == mod || i % next == next - mod) {
                    sb.append(s.charAt(i));
                }
            }
            mod ++;
         }
        return sb.toString();
    }
}