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".

思路：主要是如何将string中的序号转换成二维数组中的行列号
利用分组的思想，

public class Solution {
    public String convert(String s, int numRows) {
        //不要用二维数组存储，原样输出即可
        if(s.length() <= numRows || numRows == 1){
            return s;
        }
        //需要使用二维数组存储
        int row = numRows;
        int col1 = s.length()/(2*(numRows-1));
        int col2 = s.length()%(2*(numRows-1));
        int col = 0;
        if(col2 <= numRows){
            col = (numRows - 1 ) * col1 + 1;  
        }else{
            col = (numRows - 1 ) * col1 + 1 + col2 - numRows;
        }

        char[][] arr = new char[row][col];
        int count = 2*(numRows-1);
        for(int k = 0; k < s.length(); k ++){
            //组号
            int group = k / count;
            //组内序号
            int rankInGroup = k % count;
            int r  = 0;
            int c = 0;
            //根据组号和组内序号转换出row和col
            if(rankInGroup <= numRows - 1){
                r = rankInGroup;
                c = (numRows - 1)*group; 
            }else{
                c = (numRows - 1) * group + 1 + rankInGroup - numRows;
                r = 2 * numRows - rankInGroup - 2;
            }
            //System.out.println("r="+r+";c="+c);
            arr[r][c] = s.charAt(k);
        }

        StringBuffer result = new StringBuffer();
        for(int i1 = 0; i1 < row; i1 ++){
            for(int j1=0; j1 < col; j1++){
                if(arr[i1][j1] != 0){
                    result.append(arr[i1][j1]);
                }
            }
        }
        return result.toString();
    }
}

改进，可以使用链表存储每一行的信息，这样存储空间为缩小