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)

  1. P   A   H   N
  2. A P L S I I G
  3. 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:

  1. string convert(string text, int nRows);

convert("PAYPALISHIRING", 3) should return "PAHNAPLSIIGYIR".

Solution:

  1. public class Solution {
  2.   public String convert(String s, int nRows) {
  3.     if (nRows == 1) 
  4.       return s;
  6.     List<StringBuilder> list = new ArrayList<>();
  8.     for (int i = 0; i < nRows; i++) {
  9.       list.add(new StringBuilder());
  10.     }
  12.     int row = 0, dir = 0;
  13.     for (int i = 0; i < s.length(); i++) {
  14.       list.get(row).append(s.charAt(i));
  16.       if (row == 0) dir = 1;
  17.       if (row == nRows - 1) dir = -1;
  19.       row += dir;
  20.     }
  22.     StringBuilder res = new StringBuilder();
  23.     for (StringBuilder sb : list) {
  24.       res.append(sb.toString());
  25.     }
  26.     return res.toString();
  27.   }
  28. }