LeetCode | ZigZag Conversion

题目

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" .

分析

注意索引值得转换关系，用nRows个StringBuilder辅助构造。

代码

public class ZigZagConversion {
	public String convert(String s, int nRows) {
		int blockSize = 2 * nRows - 2;
		if (blockSize == 0) {
			return s;
		}
		StringBuilder[] sb = new StringBuilder[nRows];
		for (int i = 0; i < nRows; ++i) {
			sb[i] = new StringBuilder();
		}
		for (int i = 0; i < s.length(); ++i) {
			int innerIndex = i % blockSize;
			if (innerIndex < nRows) {
				sb[innerIndex].append(s.charAt(i));
			} else {
				sb[nRows - 2 - (innerIndex - nRows)].append(s.charAt(i));
			}
		}
		StringBuilder result = new StringBuilder();
		for (int i = 0; i < nRows; ++i) {
			result.append(sb[i]);
		}
		return result.toString();
	}
}