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".

大意就是把给定的字符串倒N字形打印，(原意是锯齿状，怎么也联想不出来是倒N字，纠结了好久)

public String convert(String s, int numRows) {
        char[] charArray = s.toCharArray();

        StringBuilder[] sbArray = new StringBuilder[numRows];
        /**
         * 由给定例子可以知道，numRows代表了行数，我们实例化numRows个stringbuilder用来存储每一行的字符
         * 这样最终结果只要将stringbuilder拼接就可以得到
         */
        for(int i = 0;i < numRows; i++){
            sbArray[i] = new StringBuilder("");
        }

        int i = 0 ;

        while(i < charArray.length){
            /**
             * 打印倒N字形的垂直自上向下部分
             * 依次填充至sbarray中
             */
            for(int idx = 0; i < charArray.length && idx < numRows; idx ++){
                sbArray[idx].append(charArray[i++]);
            }
            /**
             * 打印倒N字形自底向斜上部分
             * 依次填充至sbarray中,除首尾行之外
             */
            for(int idx = numRows - 2; i < charArray.length && idx > 0; idx --){
                sbArray[idx].append(charArray[i++]);
            }
        }
        /**
         * 拼接得到答案
         */
        for(int idx = 1;idx < numRows; idx++){
            sbArray[0].append(sbArray[idx]);
        }
        return sbArray[0].toString();
    }