[leetcode] 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".

https://oj.leetcode.com/problems/zigzag-conversion/

思路：找规律。每个zigzag是2*rows-1个字符。

public class Solution {
	public String convert(String s, int nRows) {
		if (nRows == 1)
			return s;
		StringBuilder sb = new StringBuilder();
		int len = s.length();
		for (int i = 0; i < nRows; i++) {
			if (i == 0 || i == nRows - 1) {
				int j = i;
				while (j < len) {
					sb.append(s.charAt(j));
					j += 2 * nRows - 2;
				}
			} else {
				int j = i;
				int k = 2 * nRows - 2 - i;
				while (j < len || k < len) {
					if (j < len)
						sb.append(s.charAt(j));
					if (k < len)
						sb.append(s.charAt(k));
					j += 2 * nRows - 2;
					k += 2 * nRows - 2;
				}
			}

		}
		return sb.toString();

	}

	public static void main(String[] args) {
		System.out.println(new Solution().convert("PAYPALISHIRING", 3));
		System.out.println(new Solution().convert("abcdefghijklmn", 5));
		System.out.println(new Solution().convert("abcdefghijklmn", 4));
		System.out.println(new Solution().convert("abcdefghijklmn", 1));

	}

}

第二遍记录：比较无聊的数学题，关键在于推算坐标。坐标分为两种，一种是竖直的，一种是斜向的。建议多画集中情况具体分析下。 

参考：

http://fisherlei.blogspot.com/2013/01/leetcode-zigzag-conversion.html

http://blog.csdn.net/linhuanmars/article/details/21145039