ZigZag Conversion

ZigZagConversion.java

/**
 * 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".
 */

public class Solution {
    public String convert(String s, int nRows) {
        if(nRows <= 1)
            return s;
        StringBuilder[] list = new StringBuilder[nRows];
        for(int i = 0; i < nRows; i++)
            list[i] = new StringBuilder();
        int row = 0;
        int i = 0;
        boolean down = true;
        while(i < s.length()){
            list[row].append(s.charAt(i));
            if(row == 0)
                down = true;
            if(row == nRows - 1)
                down = false;
            if(down)
                row++;
            else
                row--;
            i++;
        }
        StringBuilder res = new StringBuilder();
        for(StringBuilder sb : list)
            res.append(sb.toString());
        return res.toString();
    }
}