doubly linked list

258/doublyLinkedList/DoublyLinkedList.java

@@ -0,0 +1,175 @@
+import java.util.NoSuchElementException;
+
+/**
+ * An implementation of the Linked List data structure.
+ *
+ * The LinkedList is like the ArrayList, except the list's
+ * elements are stored in linked nodes instead of an array.
+ *
+ * @param <E> component type
+ */
+public class DoublyLinkedList<E> {
+
+    public static void main(String[] args) {
+        DoublyLinkedList<Integer> list = new DoublyLinkedList<>();
+        for (int i = 2; i <= 20; i += 2) list.add(i);
+
+        System.out.println(list);
+
+        list.removeFirst();
+
+        list.removeLast();
+
+        list.printReverse();
+    }
+
+    // The list's elements are stored in nodes.
+    private class Node {
+
+        E element; // Element stored in this node
+        Node next; // Link to the next node in the list
+        Node previous; // Link to the previous node in the list
+    }
+
+    private Node head; // Link to the first node
+    private Node tail; // Link to the last node
+    private int size; // Number of elements in the list
+
+    public void add(E elem) {
+        Node n = new Node();
+        n.element = elem;
+        if (head == null) head = tail = n;
+        else {
+            n.previous = tail;
+            tail.next = n;
+            tail = n;
+        }
+        size++;
+    }
+
+    public void add(int index, E elem) {
+        if (index < 0 || index > size) throw new IndexOutOfBoundsException(
+            index + ""
+        );
+
+        Node n = new Node();
+        n.element = elem;
+
+        if (index == 0) {
+            n.next = head;
+            head = n;
+            if (tail == null) tail = n;
+        } else {
+            Node walker = head;
+            for (int i = 0; i < index - 1; i++) {
+                walker = walker.next;
+            }
+
+            n.next = walker.next;
+            walker.next = n;
+
+            if (n.next == null) tail = n;
+        }
+
+        size++;
+    }
+
+    public E get(int index) {
+        if (index < 0 || index >= size) throw new IndexOutOfBoundsException(
+            index + ""
+        );
+        Node walker = head;
+        for (int i = 0; i < index; i++) walker = walker.next;
+        return walker.element;
+    }
+
+    public void set(int index, E element) {
+        if (index < 0 || index >= size) throw new IndexOutOfBoundsException(
+            index + ""
+        );
+        Node walker = head;
+        for (int i = 0; i < index; i++) walker = walker.next;
+
+        walker.element = element;
+    }
+
+    public E get(E element) {
+        Node walker = head;
+        for (int i = 0; i < size; i++) {
+            if (walker.element.equals(element)) {
+                return walker.element;
+            }
+
+            walker = walker.next;
+        }
+
+        return null;
+    }
+
+    public boolean contains(E element) {
+        Node walker = head;
+        for (int i = 0; i < size; i++) {
+            if (walker.element.equals(element)) {
+                return true;
+            }
+
+            walker = walker.next;
+        }
+
+        return false;
+    }
+
+    public int size() {
+        return size;
+    }
+
+    public void removeFirst() {
+        if (size == 0) throw new NoSuchElementException();
+
+        if (size == 1) {
+            head = tail = null;
+        } else {
+            head = head.next;
+            head.previous = null;
+        }
+
+        size--;
+    }
+
+    public void removeLast() {
+        if (size == 0) throw new NoSuchElementException();
+
+        if (size == 1) {
+            head = tail = null;
+        } else {
+            tail = tail.previous;
+            tail.next = null;
+        }
+
+        size--;
+    }
+
+    public void printReverse() {
+        Node walker = tail;
+        while (walker != null) {
+            System.out.println(walker.element);
+
+            walker = walker.previous;
+        }
+    }
+
+    @Override
+    public String toString() {
+        if (head == null) return "[]";
+        else {
+            String s = "[";
+            Node walker = head;
+            while (walker != tail) {
+                s += walker.element + ", ";
+                walker = walker.next;
+            }
+            s += tail.element + "]";
+            return s;
+        }
+    }
+}

258/linkedListLab/LinkedList.java

@@ -37,6 +37,33 @@ public class LinkedList<E> {
         size++;
     }
 
+    public void add(int index, E elem) {
+        if (index < 0 || index > size) throw new IndexOutOfBoundsException(
+            index + ""
+        );
+
+        Node n = new Node();
+        n.element = elem;
+
+        if (index == 0) {
+            n.next = head;
+            head = n;
+            if (tail == null) tail = n;
+        } else {
+            Node walker = head;
+            for (int i = 0; i < index - 1; i++) {
+                walker = walker.next;
+            }
+
+            n.next = walker.next;
+            walker.next = n;
+
+            if (n.next == null) tail = n;
+        }
+
+        size++;
+    }
+
     public E get(int index) {
         if (index < 0 || index >= size) throw new IndexOutOfBoundsException(
             index + ""