Java [leetcode 6] ZigZag Conversion

问题描述：

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".

解题思路：

注意到zigzag的字符串按照读写的顺序是来回分配给不同行的，所以存在取模值的问题，对于正着往下读的字符串，对(nRows-1)取模值的结果刚好是它对应的行数，而对于往上读取的情况，对(nRows-1)取模的结果加上行号刚好等于(nRows-1)。所以考虑用boolean变量记录方向。对于每一行设立StringBuilder对象，适合向其末尾追加值。

代码如下：

public class Solution {

    public String convert(String s, int nRows) {

        StringBuilder[] stringBuilder = new StringBuilder[nRows];

		for(int i = 0; i < nRows; i++)

			stringBuilder[i] = new StringBuilder();

		boolean reverse = true;

		if(nRows == 1)

			return s;

		if (s.length() == 1)

			return s;

		for(int i = 0; i < s.length(); ++i){

			if(i % (nRows - 1) == 0)

				reverse = !reverse;

			if(! reverse){

				stringBuilder[i % (nRows - 1)].append(s.charAt(i));

			}

			else{

				stringBuilder[nRows - 1 -(i % (nRows - 1))].append(s.charAt(i));

			}

		}

		for(int i = 1; i < nRows; i++){

			stringBuilder[0].append(stringBuilder[i]);

		}

		return stringBuilder[0].toString();

    }

}