Package g0001_0100.s0006_zigzag_conversion

Class Solution

java.lang.Object

g0001_0100.s0006_zigzag_conversion.Solution

public class Solution
extends java.lang.Object

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

To solve the Zigzag Conversion problem in Java using a Solution class, we’ll follow these steps:

1. Define a Solution class with a method named convert.
2. Create an array of strings to represent each row of the zigzag pattern.
3. Initialize variables to keep track of the current row (row) and the direction of traversal (down).
4. Iterate through each character in the input string s.
   • Append the current character to the string representing the current row.
   • If we reach the first or last row, change the direction of traversal accordingly.
   • Update the current row based on the direction of traversal.
5. Concatenate the strings representing each row to form the final zigzag conversion.
6. Return the concatenated string.
7. Handle edge cases where the number of rows is 1 or the input string is empty.

Here’s the implementation:

public class Solution {

    public String convert(String s, int numRows) {
        if (numRows == 1 || s.length() <= numRows) {
            return s;
        }

        StringBuilder[] rows = new StringBuilder[numRows];
        for (int i = 0; i < numRows; i++) {
            rows[i] = new StringBuilder();
        }

        int row = 0;
        boolean down = false;

        for (char c : s.toCharArray()) {
            rows[row].append(c);
            if (row == 0 || row == numRows - 1) {
                down = !down;
            }
            row += down ? 1 : -1;
        }

        StringBuilder result = new StringBuilder();
        for (StringBuilder sb : rows) {
            result.append(sb);
        }

        return result.toString();
    }

    public static void main(String[] args) {
        Solution solution = new Solution();

        // Test cases
        String s1 = "PAYPALISHIRING";
        int numRows1 = 3;
        System.out.println("Example 1 Output: " + solution.convert(s1, numRows1));

        String s2 = "PAYPALISHIRING";
        int numRows2 = 4;
        System.out.println("Example 2 Output: " + solution.convert(s2, numRows2));

        String s3 = "A";
        int numRows3 = 1;
        System.out.println("Example 3 Output: " + solution.convert(s3, numRows3));
    }
}

This implementation provides a solution to the Zigzag Conversion problem in Java.

Constructor Summary

Constructors

Constructor	Description
Solution()

Method Summary

Modifier and Type	Method	Description
java.lang.String	convert(java.lang.String s, int numRows)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

Solution

public Solution()

Method Details

convert

public java.lang.String convert(java.lang.String s,
 int numRows)