added Doubly Linked List [JAVA] Fixes #824

doubly_linked_list/doublyLinkedList.java

@@ -0,0 +1,172 @@
+public class DoublyLinkedList {
+
+    protected Node firstNode;
+    protected Node lastNode;
+    protected int size;
+
+    public DoublyLinkedList(){this.size=0;}
+
+    public void getLastNode(){
+        Node temp = firstNode;
+        while(temp.next != null){
+            temp = temp.next;
+        }
+        lastNode = temp;
+    }
+
+    public void insertFirst(Object val){
+        Node node = new Node(val);
+        node.next = firstNode;
+        node.prev = null;
+        if (firstNode != null) {
+            firstNode.prev = node;
+        }
+        firstNode = node;
+        size ++;
+    }
+
+    public void insertLast(Object val){
+        getLastNode();
+        Node newNode = new Node(val);
+        lastNode.next = newNode;
+        newNode.prev = lastNode;
+        size++;
+    }
+
+    public void checkpos(int pos){
+        if(pos<0 || pos>size){
+            System.out.println("Wrong Position Entered");
+            System.exit(0);
+        }
+    }
+
+    public void checkposition(int pos){
+        if(pos<0 || pos>=size){
+            System.out.println("Wrong Position Entered");
+            System.exit(0);
+        }
+    }
+
+    public void add(int pos, Object val){
+        checkpos(pos);
+        Node newNode = new Node(val);
+        Node temp = firstNode;
+        if(pos == 0){
+            insertFirst(val);
+        }else {
+            while (pos-- > 1) {
+                temp = temp.next;
+            }
+            newNode.next = temp.next;
+            if(temp.next !=null){
+                temp.next.prev = newNode;}
+            newNode.prev = temp;
+            temp.next = newNode;
+            size++;
+        }
+    }
+
+    public int size(){
+        return size;
+    }
+
+    public void display(){
+        Node temp = firstNode;
+        System.out.print("START ");
+        while(temp != null){
+            System.out.print(temp.data+" <-> ");
+            temp = temp.next;
+        }
+        System.out.print("END\n");
+    }
+
+    public Object get(int pos){
+        checkposition(pos);
+        Node temp = firstNode;
+        while(pos-- >0){
+            temp = temp.next;
+        }
+        return temp.data;
+    }
+
+    public Object remove(int pos){
+        checkposition(pos);
+        Node temp = firstNode;
+        Node RE = new Node();
+        if(pos == 0){
+            RE = firstNode;
+            firstNode = temp.next;
+            temp.next.prev = null;
+            size--;
+            return RE.data;
+        }
+        else if(pos == size - 1){
+            getLastNode();
+            RE = lastNode;
+            temp = lastNode;
+            lastNode = temp.prev;
+            temp.prev.next = null;
+            size--;
+            return RE.data;
+        }
+        while(pos-- > 1){
+            temp = temp.next;
+        }
+        RE = temp.next;
+        temp.next = temp.next.next;
+        temp.next.prev = temp;
+        size--;
+        return RE.data;
+    }
+
+    public void reverseDisplay(){
+        getLastNode();
+        Node last = lastNode;
+        System.out.print("START ");
+        while(last != null){
+            System.out.print(last.data+" <-> ");
+            last = last.prev;
+        }
+        System.out.print("END\n");
+    }
+
+    public static void main(String[] args) {
+        DoublyLinkedList d = new DoublyLinkedList();
+        d.insertFirst(21);
+        d.insertFirst(23);
+        d.insertFirst(24);
+        d.add(3,"hello");
+        d.display();
+        System.out.println("Size of the list is: "+ d.size());
+        System.out.println("Removing Element");
+        System.out.println(d.remove(3)); //displays the removed element
+        d.display(); //displays the list after removal
+        d.add(1,"hello"); //adds hello at 1st index
+        d.insertLast(54);
+        d.insertLast(421);
+        System.out.println("After adding few more elements");
+        d.display();
+        System.out.println("Size of the list is: "+ d.size());
+        System.out.println("Get Element at 0"+d.get(0));
+        System.out.println("Reverse the List");
+        d.reverseDisplay();
+    }
+}
+
+class Node {
+    Object data;
+    Node next;
+    Node prev;
+
+    public Node() {}
+
+    public Node(Object value) {
+        this.data = value;
+    }
+
+    public Node(Object value, Node next, Node prev) {
+        this.data = value;
+        this.next = next;
+        this.prev = prev;
+    }
+}