docs: add Hacktoberfest documentation contribution guide

docs/Hacktoberfest_Guide.md

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+# Hacktoberfest Documentation Contribution Guide
+
+👋 Welcome contributors!  
+This repository focuses on **documentation-only** contributions.
+
+## ✅ What You Can Contribute
+- Fix typos or grammar in README files  
+- Add short explanations to existing documentation  
+- Improve formatting (headings, code blocks, etc.)  
+- Add contribution tips for beginners  
+
+## 🚀 How to Contribute
+1. Fork this repository  
+2. Create a new branch: `docs/update-readme`  
+3. Make your changes  
+4. Open a Pull Request with the title:  
+   **"docs: improve documentation clarity"**
+
+Thank you for contributing to open-source documentation!

removeZeros.java

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+/*
+LeetCode Problem: Remove Zeros from a Number
+--------------------------------------------
+Description:
+Given a number n, remove all the zeros from it and return the resulting number.
+
+Example:
+Input: n = 102030
+Output: 123
+
+Approach:
+Convert the number to a string, remove all '0' characters using String.replace(),
+and parse the result back to a long.
+
+Time Complexity: O(d), where d is the number of digits.
+Space Complexity: O(d)
+*/
+
+class Solution {
+    public long removeZeros(long n) {
+        String str = String.valueOf(n);
+        String res = str.replace("0", "");
+        return Long.parseLong(res);
+    }
+
+    public static void main(String[] args) {
+        Solution s = new Solution();
+        System.out.println(s.removeZeros(102030)); // Output: 123
+    }
+}