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Added LinkedList problems
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‎README.md‎

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Computer Science problems in Java.
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### Topics covered
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1. LinkedList
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1. Fast and Slow Pointer
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1. Midpoint of LinkedList
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2. Nth element removal from the end of the list
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## Backlog
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### Problems
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2. You have N cars numbered from 1 to N. Car 1 is open and all the other cars are closed. Each car has a list of keys
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where key i can open the car i. Find out if we can open all the cars.
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### Design
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1. LLD of chess
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### Patterns
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1. Two Pointers
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* Batch framework for Java — https://github.com/j-easy/easy-batch
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* Object-functional extension for Java — https://github.com/vavr-io/vavr
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* Java binary serialization and cloning — https://github.com/EsotericSoftware/kryo
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### Design
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1. LLD of chess
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### System Design Problems
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#### Basics
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1. Design a chess game
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2. Design a simple URL shortening service.
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3. Design a basic chat application.
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4. Design a file storage system.
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5. Design a simple social media platform.
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6. Design a simple search engine.
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7. Design a simple e-commerce website.
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8. Design a basic ride-sharing system.
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9. Design a basic video streaming service.
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10. Design a simple recommendation system.
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11. Design a basic food delivery app.
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12. Design a parking lot management system.
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13. Design a simple music streaming service.
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14. Design a basic online ticket booking system.
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15. Design a simple note-taking application.
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16. Design a weather forecasting system.
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17. Design a basic email service.
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18. Design a file synchronization system.
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19. Design a simple calendar application.
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20. Design a basic online quiz platform.
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21. Design a user authentication system.
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#### Advanced
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1. Design a URL-shortening service like bit.ly.
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2. Design a distributed key-value store like Redis.
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3. Design a scalable social network like Facebook.
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4. Design a scalable recommendation system like Netflix.
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5. Design a distributed file system like Hadoop's HDFS.
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6. Design a real-time messaging system like WhatsApp.
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7. Design a web crawler like Google.
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8. Design a distributed cache like Memcached.
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9. Design a content delivery network (CDN) like Cloudflare.
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10. Design a scalable search engine like Google.
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11. Design a ride-sharing system like Uber.
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12. Design a video streaming service like YouTube.
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13. Design an online food delivery system like Zomato.
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14. Design a collaborative document editing system like Google Docs.
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15. Design an e-commerce platform like Amazon.
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16. Design a recommendation system for an online marketplace.
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17. Design a fault-tolerant distributed database system.
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18. Design a scalable event-driven system like Twitter.
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19. Design a scalable photo-sharing platform like Instagram.
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20. Design a distributed task scheduling system.
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### Design Patterns
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#### Creational patterns
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These patterns provide various object creation mechanisms, which increase the flexibility and reuse of existing code.
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1. Factory Method
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2. Abstract Factory
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3. Builder
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4. Prototype
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5. Singleton
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#### Structural patterns
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These patterns explain how to assemble objects and classes into larger structures while keeping these structures flexible and efficient.
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1. Adapter
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2. Bridge
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3. Composite
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4. Decorator
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5. Facade
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6. Flyweight
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7. Proxy
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#### Behavioral patterns
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These patterns are concerned with algorithms and the assignment of responsibilities between objects.
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1. Chain of Responsibility
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2. Command
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3. Iterator
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4. Mediator
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5. Memento
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6. Observer

‎src/main/java/org/dojo/leetcode/LinkedListProblems.java‎

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import static org.dojo.leetcode.SinglyLinkedList.SinglyLinkedListNode;
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public class LinkedListProblems {
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public static class ListNode {
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int val;
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ListNode next;
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ListNode() { }
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ListNode(int val) { this.val = val; }
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ListNode(int val, ListNode next) {
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this.val = val;
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this.next = next;
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}
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}
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public SinglyLinkedListNode addTwoNumbers(SinglyLinkedListNode l1, SinglyLinkedListNode l2) {
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var carryover = 0;
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var sumNode = new SinglyLinkedListNode();
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return result;
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}
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public ListNode removeNthFromEnd(ListNode head, int n) {
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ListNode slow = head, fast = head;
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int count = 1;
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for (int i = 0; i < n; i++) {
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if (fast.next == null) break;
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fast = fast.next;
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count++;
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}
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if (count == n) return head.next;
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while (fast.next != null) {
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slow = slow.next;
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fast = fast.next;
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}
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slow.next = slow.next.next;
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return head;
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}
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public void deleteNode(ListNode node) {
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node.val = node.next.val;
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node.next = node.next.next;
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}
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}

‎src/test/java/org/dojo/leetcode/LinkedListProblemsTests.java‎

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package org.dojo.leetcode;
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import org.dojo.leetcode.LinkedListProblems.ListNode;
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import org.dojo.leetcode.SinglyLinkedList.SinglyLinkedListNode;
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import org.junit.jupiter.params.ParameterizedTest;
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import org.junit.jupiter.params.provider.Arguments;
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import java.util.stream.Stream;
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import static org.junit.jupiter.api.Assertions.assertEquals;
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import static org.junit.jupiter.api.Assertions.assertNotNull;
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import static org.junit.jupiter.api.Assertions.assertNull;
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class LinkedListProblemsTests {
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private final LinkedListProblems sut = new LinkedListProblems();
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actual = actual.getNext();
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}
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}
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private static ListNode linkedListNodeFromArray(int[] arr) {
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if (arr == null || arr.length == 0) return null;
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ListNode head = new ListNode(arr[0]);
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ListNode current = head;
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for (int i = 1; i < arr.length; i++) {
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ListNode newNode = new ListNode(arr[i]);
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current.next = newNode;
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current = newNode;
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}
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return head;
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}
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private static Stream<Arguments> removeNthFromEndTestData() {
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return Stream.of(
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Arguments.of(
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linkedListNodeFromArray(new int[] {1, 2, 3, 4, 5}),
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2,
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linkedListNodeFromArray(new int[] {1, 2, 3, 5})
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),
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Arguments.of(
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linkedListNodeFromArray(new int[] {1}),
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1,
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null
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),
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Arguments.of(
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linkedListNodeFromArray(new int[] {1, 2}),
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1,
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linkedListNodeFromArray(new int[] {1})
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),
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Arguments.of(
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linkedListNodeFromArray(new int[] {1, 2, 3}),
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3,
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linkedListNodeFromArray(new int[] {2, 3})
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),
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Arguments.of(
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linkedListNodeFromArray(new int[] {1, 2, 3, 4, 5, 6}),
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3,
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linkedListNodeFromArray(new int[] {1, 2, 3, 5, 6})
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)
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);
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}
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@ParameterizedTest
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@MethodSource("removeNthFromEndTestData")
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void removeNthFromEnd(ListNode head, int n, ListNode expectedList) {
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ListNode actual = sut.removeNthFromEnd(head, n);
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if (expectedList == null) {
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assertNull(actual);
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return;
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}
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ListNode expected = expectedList;
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while (expected != null) {
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assertNotNull(actual, "Actual list is shorter than expected");
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assertEquals(expected.val, actual.val);
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expected = expected.next;
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actual = actual.next;
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}
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assertNull(actual, "Actual list is longer than expected");
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}
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}

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