ZigZag Conversion

题目描述

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".

ZigZag 是这个意思：

解题思路

研究后发现：

• numRows==1 时，直接返回 s；
• numRows > 1 时，第一行的数字索引为差值为 2*numRows-2：
  • 所以相应第二行的索引为第一行索引'+/-1'；
  • 第三行索引是'+/-2'；
  • ...

代码

class Solution {
    public String convert(String s, int numRows) {
        if (s == null || s.length() == 0 || numRows == 1)
            return s;
        StringBuilder ret = new StringBuilder();
        for (int i = 0; i < numRows; i++) {
            for (int j = 0; j < s.length()+(2*numRows-2); j = j+(2*numRows-2)) {
                if (j != 0 && i != 0 && i < numRows-1 && j-i < s.length())
                    ret.append(s.charAt(j-i));
                if (j+i < s.length())
                    ret.append(s.charAt(j+i));
            }
        }
        return ret.toString();
    }
}