LeetCode#6 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”.

       第一次看到这个题目的人，可能不知道ZigZag是什么意思，简单解释一下，就是把字符串原顺序012345……按下图所示排列：

这道题找规律即可，循环周期可能比较容易找，周期中间的规律 2 * nRows - 2 - 2 * i 可能不大好找。

public class Solution {      public String convert(String s, int nRows) {          int len = s.length();          if (len == 0 || nRows < 2) return s;          String ret = "";          int lag = 2*nRows - 2; //循环周期          for (int i = 0; i < nRows; i++) {              for (int j = i; j < len; j += lag) {                  ret += s.charAt(j);                  //非首行和末行时还要加一个                  if (i > 0 && i < nRows-1) {                      int t = j + lag - 2*i;                      if (t < len) {                          ret += s.charAt(t);                      }                  }              }          }          return ret;      }  }