题解 | #牛牛的旗语传递#

import java.util.*;


public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     *
     * @param s string字符串
     * @param numRows int整型
     * @return string字符串
     */
    public String decodeFlag (String s, int numRows) {
        // write code here
        StringBuilder sb = new StringBuilder();
        int lie = s.length();
        char[][] charS = new char[numRows][lie];
        for(int i = 0;i < numRows;i++){
            for(int j = 0;j < lie;j++){
                charS[i][j] = '#';
            }
        }
        int j = 0;
        int row = 0;
        boolean flag = true;
        for (int k = 0; k < s.length(); k++) {
            charS[row][j] = s.charAt(k);

            if (flag) {
                row++;
                if (row == numRows) {
                    flag = false;
                    j++;
                    row = numRows -2;
                   
                }
            } else {
                row--;
                if (row == -1) {
                    flag = true;
                    j++;
                    row = 1;
                }
            }
        }

        for (int i = 0; i < numRows; i++) {
            for (int k = 0; k < lie; k++) {
                if (charS[i][k] != '#')
                    sb.append(charS[i][k]);
            }
        }
        return sb.toString();
    }
}