每日力扣：6. Z 字形变换

package com.sample.suncht.algo;

import java.util.ArrayList;
import java.util.List;

/**
 * 6. Z 字形变换
 * 

 * 将一个给定字符串根据给定的行数，以从上往下、从左到右进行 Z 字形排列。
 * 

 * 比如输入字符串为 "LEETCODEISHIRING" 行数为 3 时，排列如下：
 * 

 * L   C   I   R
 * E T O E S I I G
 * E   D   H   N
 * 之后，你的输出需要从左往右逐行读取，产生出一个新的字符串，比如："LCIRETOESIIGEDHN"。
 *
 * 时间复杂度：O(n), 空间复杂度：O(n)
 * @author sunchangtan
 * @date 2019/3/6 11:46
 */
public class ZigzagConversion {
    public String convert(String s, int numRows) {
        if (s == null) {
            return "";
        }
        if (numRows <= 1) {
            return s;
        }

        char[] chars = s.toCharArray();
        int len = chars.length;
        if(numRows > len) {
            return s;
        }

        StringBuilder builder = new StringBuilder("");

        for (int i = 0; i < numRows; i++) {
            int span1 = 2 * (numRows - i - 1);
            int span2 = 2 * i;
            int index = i;
            int counter = 0;
            do {
                if(counter % 2 == 0) {
                    if(span1 > 0) {
                        builder.append(chars[index]);
                        index = index + span1;
                    }
                } else {
                    if(span2 > 0) {
                        builder.append(chars[index]);
                        index = index + span2;
                    }
                }
                counter++;
            } while (index < len);
        }

        return builder.toString();
    }

    public static void main(String[] args) {
        List> datas = new ArrayList<>();
        datas.add(new AlgoHelper.BiInputParams<>("LEETCODEISHIRING", 2, "LECDIHRNETOESIIG"));
        datas.add(new AlgoHelper.BiInputParams<>("LEETCODEISHIRING", 3, "LCIRETOESIIGEDHN"));
        datas.add(new AlgoHelper.BiInputParams<>("LEETCODEISHIRING", 4, "LDREOEIIECIHNTSG"));
        datas.add(new AlgoHelper.BiInputParams<>("LEETCODEISHIRING", 5, "LIEESGEDHNTOIICR"));
        datas.add(new AlgoHelper.BiInputParams<>("LEETCODEISHIRING", 6, "LHESIEIRTEICDNOG"));
        datas.add(new AlgoHelper.BiInputParams<>("LEETCODEISHIRING", "LEETCODEISHIRING".length(), "LEETCODEISHIRING"));
        datas.add(new AlgoHelper.BiInputParams<>("LEETCODEISHIRING", 1, "LEETCODEISHIRING"));
        datas.add(new AlgoHelper.BiInputParams<>("LEETCODEISHIRING", 20, "LEETCODEISHIRING"));

        AlgoHelper.assertResult(datas, new ZigzagConversion()::convert);
    }
}