LeetCode | 易学教程

Topic

String

Description

https://leetcode.com/problems/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 s, int numRows);

Example 1:

Input: s = "PAYPALISHIRING", numRows = 3
Output: "PAHNAPLSIIGYIR"

Example 2:

Input: s = "PAYPALISHIRING", numRows = 4
Output: "PINALSIGYAHRPI"
Explanation:
P     I    N
A   L S  I G
Y A   H R
P     I

Example 3:

Input: s = "A", numRows = 1
Output: "A"

Constraints:

1 <= s.length <= 1000
s consists of English letters (lower-case and upper-case), ',' and '.'.
1 <= numRows <= 1000

Analysis

分析Example 2，Input: s = "PAYPALISHIRING", numRows = 4

            3           3
group     2   2       2   2
        1       1   1        1     1
      0           0             0
index 0 1 2 3 4 5 6 7 8 9 10 11 12 13
  s   P A Y P A L I S H I R  I  N  G

按group号，分别收集字符，最后到汇总输出。

Submission

public class ZigZagConversion {
	public String convert(String s, int numRows) {
		StringBuilder[] sbs = new StringBuilder[numRows];

		boolean upDownflag = true;
		int sbsPointer = 0;
		int halfCycle = numRows - 1;

		for (int i = 0; i < s.length(); i++) {
			if (sbs[sbsPointer] == null)
				sbs[sbsPointer] = new StringBuilder();

			sbs[sbsPointer].append(s.charAt(i));

			if (halfCycle != 0) {
				if (upDownflag && sbsPointer + 1 > halfCycle) {
					upDownflag = false;
				}
				if (!upDownflag && sbsPointer - 1 < 0) {
					upDownflag = true;
				}
				sbsPointer = upDownflag ? sbsPointer + 1 : sbsPointer - 1;
			}
		}

		for (int i = 1; i < numRows; i++) {
			if (sbs[i] == null)
				break;
			sbs[0].append(sbs[i]);
		}

		return sbs[0].toString();
	}
}

Test

import static org.junit.Assert.*;
import org.junit.Test;

public class ZigZagConversionTest {

	@Test
	public void test() {
		ZigZagConversion obj = new ZigZagConversion();

		assertEquals("PAHNAPLSIIGYIR", obj.convert("PAYPALISHIRING", 3));
		assertEquals("PINALSIGYAHRPI", obj.convert("PAYPALISHIRING", 4));
		assertEquals("A", obj.convert("A", 1));
		assertEquals("AB", obj.convert("AB", 1));
		
	}
}

来源：oschina

链接：https://my.oschina.net/jallenkwong/blog/4869801

标签

junit

java