Add Zigzag Conversion

Author: thanthtooaung-coding

README.md

@@ -6,7 +6,7 @@ This repository contains my solutions to various LeetCode problems. Each solutio
 
 ## LeetCode Stats
 - **Profile**: [Vinnn_96](https://leetcode.com/u/Vinnn_96/)
-- **Problems Solved**: 7
+- **Problems Solved**: 8
 - **Languages**: Java
 
 ## Repository Structure
@@ -24,14 +24,15 @@ Each problem has its own directory containing:
 | 3 | [Longest Substring Without Repeating Characters](Longest%20Substring%20Without%20Repeating%20Characters) | Medium | [Java](Longest%20Substring%20Without%20Repeating%20Characters/Solution.java) | Hash Table, String, Sliding Window |
 | 4 | [Median of Two Sorted Arrays](Median%20of%20Two%20Sorted%20Arrays) | Hard | [Java](Median%20of%20Two%20Sorted%20Arrays/Solution.java) | Array, Binary Search, Divide and Conquer |
 | 5 | [Longest Palindromic Substring](Longest%20Palindromic%20Substring) | Medium | [Java](Longest%20Palindromic%20Substring/Solution.java) | Two Pointers, String, Dynamic Programming |
+| 6 | [Zigzag Conversion](Zigzag%20Conversion) | Medium | [Java](Zigzag%20Conversion/Solution.java) | String |
 | 214 | [Shortest Palindrome](Shortest%20Palindrome) | Hard | [Java](Shortest%20Palindrome/Solution.java) | String, Rolling Hash, String Matching, Hash Function |
 | 2924 | [Find Champion II](Find%20Champion%20II) | Medium | [Java](Find%20Champion%20II/Solution.java) | Graph |
 
 ## Categories
 
 ### By Difficulty
 - Easy: 1
-- Medium: 4
+- Medium: 5
 - Hard: 2
 
 ### By Topics
@@ -44,6 +45,7 @@ Each problem has its own directory containing:
 - String Problems
   - [Longest Substring Without Repeating Characters](Longest%20Substring%20Without%20Repeating%20Characters)
   - [Longest Palindromic Substring](Longest%20Palindromic%20Substring)
+  - [Zigzag Conversion](Zigzag%20Conversion)
   - [Shortest Palindrome](Shortest%20Palindrome)
 - Dynamic Programming Problems
   - [Longest Palindromic Substring](Longest%20Palindromic%20Substring)

Zigzag Conversion/README.md

@@ -0,0 +1,50 @@
+# Zigzag Conversion
+
+## LeetCode Problem
+- Problem Number: 6
+- Problem Link: https://leetcode.com/problems/zigzag-conversion/
+- Difficulty: Medium
+- Topics: String
+
+## Problem Description
+The string "PAYPALISHIRING" is written in a zigzag pattern on a given number of rows like this:
+
+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);
+
+## Examples
+
+### 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), digits, and spaces.
+- 1 <= numRows <= 1000

Zigzag Conversion/Solution.java

@@ -0,0 +1,30 @@
+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 currentRow = 0;
+        boolean goingDown = false;
+
+        for (char c : s.toCharArray()) {
+            rows[currentRow].append(c);
+            if (currentRow == 0 || currentRow == numRows - 1) {
+                goingDown = !goingDown;
+            }
+            currentRow += goingDown ? 1 : -1;
+        }
+
+        StringBuilder result = new StringBuilder();
+        for (StringBuilder row : rows) {
+            result.append(row);
+        }
+
+        return result.toString();
+    }
+}