Practice some linkedlist questions

src/advance/linkedlist/Play.java

@@ -2,156 +2,150 @@
 
 public class Play {
 
-    private Node head;
-    private Node tail;
+    private class ListNode {
+        private ListNode next;
+        private int value;
 
-    private class Node {
-        private int data;
-        private Node next;
-        private Node prev;
-
-        public Node(int data) {
-            this.data = data;
-        }
-
-        public Node(int data, Node next) {
-            this.data = data;
-            this.next = next;
+        public ListNode(int value, ListNode node) {
+            this.value = value;
+            this.next = node;
         }
 
-        public Node() {
+        public ListNode(int value) {
+            this.value = value;
         }
 
+        @Override
         public String toString() {
-            return "Node: " + data;
+            return "value = " + value;
         }
     }
 
-    public Play() {
-    }
+    private ListNode head;
 
-    // Insert first element
-    public void insertFirstDll(int value) {
-        Node newNode = new Node(value);
+    public void addFirst(int value) {
+        ListNode newNode = new ListNode(value);
         newNode.next = head;
-        newNode.prev = null;
-
-        if (head != null)
-            head.prev = newNode;
-
         head = newNode;
     }
 
-    public void displayDll() {
-        Node temp = head;
-        while (temp != null) {
-            System.out.print(temp.data + " <-> ");
-            temp = temp.next;
-        }
-        System.out.println("END");
-    }
-
-    // Add to the end of the list
-    public void insertLastDll(int value) {
-        Node newNode = new Node(value);
-        Node lastNode = head;
+    public void addLast(int value) {
+        ListNode newNode = new ListNode(value);
         newNode.next = null;
+
         if (head == null) {
-            newNode.prev = null;
             head = newNode;
             return;
         }
-
-        while (lastNode.next != null) {
-            lastNode = lastNode.next;
+        ListNode temp = head;
+        while (temp.next != null) {
+            temp = temp.next;
         }
-        lastNode.next = newNode;
-        newNode.prev = lastNode;
+        temp.next = newNode;
     }
 
-    // Get element at an index
-    public Node getIndex(int index) {
-        Node temp = head;
-
+    // Get node given index
+    public ListNode getNode(int index) {
+        ListNode temp = head;
         for (int i = 0; i < index; i++) {
             temp = temp.next;
         }
         return temp;
     }
 
-    // Find a value in a list
-    public Node findNodeByValue(int value) {
-        Node temp = head;
-        while (temp != null) {
-            if (temp.data == value)
-                return temp;
-            temp = temp.next;
+    // Find node given the value
+    public ListNode findNode(int data) {
+        ListNode node = head;
+        while (node != null) {
+            if (node.value == data)
+                return node;
+            node = node.next;
         }
         return null;
     }
 
-    // check if the list is empty
-    public boolean isEmpty() {
-        return head == null;
-    }
-
-    // get the size of the list
-    public int sizeDll() {
-        Node temp = head;
-        int size = 0;
+    public int getLength() {
+        ListNode temp = head;
+        int length = 0;
         while (temp != null) {
-            size++;
+            length++;
             temp = temp.next;
         }
-        return size;
+        return length;
     }
 
-    public void insertAtIndex(int after, int value) {
-        Node prevNode = findNodeByValue(after);
-        if (prevNode == null) {
-            System.out.println("Node not found");
-            return;
-        }
-
-        Node newNode = new Node(value);
-        newNode.next = prevNode.next;
-        prevNode.next = newNode;
-        newNode.prev = prevNode;
-        if (newNode.next != null) {
-            newNode.next.prev = newNode;
-        }
-    }
-
-    // Return -1 if the head is null
     public int deleteFirst() {
-        if (head == null)
-            return -1;
+        if (head == null) return -1;
 
-        int data = head.data;
+        int data = head.value;
         head = head.next;
-        head.prev = null;
         return data;
     }
 
-    public int deleteLastNode(){
-        // data
-        // find lastnode
-        // move the lastnode back
-        // set the next of the lastnode to null
-        if(head == null){
-            return -1;
-        }
-        if (head.next == null){
-            int data = head.data;
-            head = null;
-            return data;
+    public int deleteLast(){
+        if (head == null) return -1;
+//        if (head.next == null){
+//            deleteFirst();
+//            return head.value;
+//        }
+        ListNode last=head;
+        int size = 1;
+        while (last.next != null){
+            size++;
+            last = last.next;
         }
-        Node lastNode = head;
-        while (lastNode.next != null){
-            lastNode = lastNode.next;
+        ListNode secondToLast=head;
+        for(int i = 0; i < size - 2; i++){
+            secondToLast = secondToLast.next;
         }
-        int data = lastNode.data;
-        lastNode.prev.next = null;
+        int data= last.value;
+        secondToLast.next = null;
         return data;
     }
+
+    public boolean detectCycle(){
+        ListNode turtle=head;
+        ListNode hare = head;
+
+        while (hare != null && hare.next != null){
+            turtle = turtle.next; // single step
+            hare = hare.next.next; // Double step
+            if (turtle == hare)
+                return true;
+
+        }
+        return false;
+    }
+
+    public void displayNodes() {
+        ListNode temp = head;
+
+        while (temp != null) {
+            System.out.print(temp.value + " -> ");
+            temp = temp.next;
+        }
+        System.out.println("END");
+    }
+
+    public static void main(String[] args) {
+        Play p = new Play();
+        p.addFirst(5);
+        p.addFirst(4);
+        p.displayNodes();
+        p.addLast(15);
+//        p.addLast(13);
+        p.displayNodes();
+        p.deleteFirst();
+        p.displayNodes();
+        p.deleteLast();
+        p.displayNodes();
+        p.deleteLast();
+        p.displayNodes();
+        p.deleteLast();
+        p.displayNodes();
+
+
+
+//        System.out.println("The length is: " + p.getLength());
+    }
 }