🚀 Add singly linked list implementation

Author: cszach

lists/LinkedList.java

@@ -0,0 +1,174 @@
+/**
+ * A class that represents a node.
+ *
+ * <p>A node contains data of any type and a pointer to the next element. To be used in a linked
+ * list implementation.
+ *
+ * @author Duong Nguyen
+ */
+class Node<T> {
+
+  T data;
+  Node next;
+
+  /**
+   * Constructs a new node in a list.
+   *
+   * @param data the data that this node contains
+   * @param next the address of the next node in the list
+   */
+  Node(T data, Node next) {
+    this.data = data;
+    this.next = next;
+  }
+}
+
+/**
+ * An implementation of a singly linked list.
+ *
+ * <p>Implementation includes methods to insert and delete at the head, the tail, and a specified
+ * index.
+ *
+ * @author Duong Nguyen
+ */
+@SuppressWarnings("unchecked")
+class LinkedList<T> {
+
+  Node<T> head;
+  Node<T> tail;
+
+  /** Constructs a new linked list with a head node. */
+  LinkedList() {
+    this.head = new Node<T>(null, null);
+    this.tail = head;
+  }
+
+  /**
+   * Returns the length of this linked list.
+   *
+   * @return the length of this linked list
+   */
+  int length() {
+    Node node = this.head;
+    int length = 0;
+
+    while (node.next != null) {
+      node = node.next;
+      length++;
+    }
+
+    return length;
+  }
+
+  boolean isValidIndex(int index) {
+    return index > -1 && index < this.length();
+  }
+
+  /**
+   * Returns the node at the specified index.
+   *
+   * @param index
+   * @return the node at the specified index
+   */
+  Node get(int index) {
+    if (!this.isValidIndex(index)) return null;
+
+    Node node = this.head.next;
+
+    for (int i = 0; i < index; i++)
+      if (node.next != null) node = node.next;
+      else return null;
+
+    return node;
+  }
+
+  /**
+   * Inserts a node with the specfied data at the beginning of this list.
+   *
+   * @param data the data that the node contains
+   * @return the inserted node
+   */
+  Node insertAtStart(T data) {
+    Node node = new Node(data, this.head.next);
+    this.head.next = node;
+
+    return node;
+  }
+
+  /**
+   * Inserts a node with the specified data at the end of this list.
+   *
+   * @param data the data that the node contains
+   * @return the inserted node
+   */
+  Node insertAtEnd(T data) {
+    Node node = new Node(data, null);
+    this.tail.next = node; // old tail
+    this.tail = node; // new tail
+
+    return node;
+  }
+
+  /**
+   * Inserts a node with the specified data at the specified index.
+   *
+   * @param data the data that the node contains
+   * @param index the index at which to insert the node
+   * @return the inserted node
+   */
+  Node insert(T data, int index) {
+    if (!this.isValidIndex(index)) return null;
+
+    Node node = new Node(data, this.get(index));
+    this.get(index - 1).next = node;
+
+    return node;
+  }
+
+  /**
+   * Deletes the first node.
+   *
+   * @return the deleted node
+   */
+  Node deleteAtStart() {
+    if (this.head == this.tail) return null;
+
+    Node node = this.head.next;
+    this.head.next = node.next;
+
+    return node;
+  }
+
+  /**
+   * Deletes the last node.
+   *
+   * @return the deleted node
+   */
+  Node deleteAtEnd() {
+    if (this.tail == this.head) return null;
+
+    Node node = this.tail;
+    Node newTail = this.get(this.length() - 2);
+    newTail.next = null;
+    this.tail = newTail;
+
+    return node;
+  }
+
+  /**
+   * Deletes the node at the specified index.
+   *
+   * @param index the index of the node to be deleted
+   * @return the deleted node
+   */
+  Node delete(int index) {
+    if (!this.isValidIndex(index)) return null;
+    if (index == 0) return this.deleteAtStart();
+
+    Node prevNode = this.get(index - 1);
+    Node node = prevNode.next;
+    prevNode.next = node.next;
+
+    return node;
+  }
+}