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

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".

字符串的弯曲转换。

要做的首先就是发现每一行的规律，可以发现，每一行有2 * nRows - 2个字符。把结果的列先加入到新的字符串中，再加入行。

    public String convert(String s, int nRows) {
        if(nRows <= 1)
            return s;
        StringBuffer buf = new StringBuffer();
        int period = 2 * nRows - 2;
        for(int i=0;i<nRows;i++){
            for(int j=i;j<s.length();j+=period){
                buf.append(s.charAt(j));
                if(i !=0 && i != nRows - 1 && j+period - 2*i <s.length())
                    buf.append(s.charAt(j+period - 2*i));
            }
        }
        return buf.toString();
    }