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Java-based LeetCode algorithm problem solutions, regularly updated

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package g0001_0100.s0006_zigzag_conversion;

// #Medium #String #2023_08_09_Time_2_ms_(99.99%)_Space_43.2_MB_(99.73%)

/**
 * 6 - Zigzag Conversion\.
 *
 * Medium
 *
 * 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`
**/
public class Solution {
    public String convert(String s, int numRows) {
        int sLen = s.length();
        if (numRows == 1) {
            return s;
        }
        int maxDist = numRows * 2 - 2;
        StringBuilder buf = new StringBuilder();
        for (int i = 0; i < numRows; i++) {
            int index = i;
            if (i == 0 || i == numRows - 1) {
                while (index < sLen) {
                    buf.append(s.charAt(index));
                    index += maxDist;
                }
            } else {
                while (index < sLen) {
                    buf.append(s.charAt(index));
                    index += maxDist - i * 2;
                    if (index >= sLen) {
                        break;
                    }
                    buf.append(s.charAt(index));
                    index += i * 2;
                }
            }
        }
        return buf.toString();
    }
}