ZigZag Conversion

public class Solution {    public String convert(String s, int nRows) {        int len = s.length();          if (len == 0 || nRows <= 1) return s;                    String[] ans = new String[nRows];          Arrays.fill(ans, "");          int row = 0, delta = 1;          for (int i = 0; i < len; i++) {              ans[row] += s.charAt(i);              row += delta;              if (row >= nRows) {                  row = nRows-2;                  delta = -1;              }              if (row < 0) {                  row = 1;                  delta = 1;              }          }                    String ret = "";          for (int i = 0; i < nRows; i++) {              ret += ans[i];          }          return ret;      }}