APCS/04 ListNode/01 ListLab1/ListLab1.java

// Name: B6-24     
// Date: 11/8/19
import java.util.*;
public class ListLab1
{
   public static void main(String[] args)
   {
      ListNode head = new ListNode("hello", null);
      head = new ListNode("foo", head);
      head = new ListNode("boo", head);
      head = new ListNode("nonsense", head);
      head = new ListNode("computer",
         	new ListNode("science",
         		new ListNode("java",
         			new ListNode("coffee", head)
         		)
         	)
         );
      print(head);
      print(head);
      
      /**** uncomment the code below for ListLab1 Assignment  ****/
      
       ListNode a = copyNode(head);
       System.out.println("The head has a value \"" + head.getValue() + "\" at "+ head);
       System.out.println("The copy of head has a value of \"" + a.getValue() + "\" at "+ a);
   // 
       System.out.print("Copy the list: ");
       ListNode copy = copyList(head);
       print(copy);
   // 
       System.out.print("The rest of the list: ");
       ListNode theRest = rest(copy);
       print(theRest);
   // 
       System.out.println("First of the rest = " + first(theRest));
       System.out.println("Second of the rest = " + second(theRest));
       ListNode p = pointerToLast(theRest);
       System.out.println("Pointer to Last = " + p.getValue()+ " at " + p);
       ListNode c = copyOfLast(theRest);
       System.out.println("Copy of Last =    " + c.getValue()+ " at " + c);
   // 
       Scanner in = new Scanner(System.in);
       System.out.print("Insert what? ");
       String x = in.next();
       theRest = insertFirst(theRest, x);
       theRest = insertLast(theRest, x);
       print(theRest);
   }
   public static void print(ListNode head)
   {
      System.out.print("[");
      while(head != null)
      {
         System.out.print(head.getValue());
         head = head.getNext();
         if(head != null)
            System.out.print(", ");
      }
      System.out.println("]");
   }
   
   /* enter your code here */
   
   // returns a new node that is a copy of the argument node.
   public static ListNode copyNode(ListNode arg) {
      ListNode copy = new ListNode(arg.getValue(), arg.getNext());
      return copy;
   }
   
   // returns a new list that is a copy of the original list.
   // this method is recursive! 
   // example call:  ListNode head2 = copyList(head);
   public static ListNode copyList(ListNode arg) {
      if (arg == null)
         return arg;
      
      return new ListNode (arg.getValue(), copyList(arg.getNext()));
   }
   
   //returns a new linked list containing copies of each node in
   //the original list except the first node, maintaining the
   //order of the original list.  It is not correct to just 
   //return a pointer to the 2nd node of the original linked
   //list.  This method is recursive.
   public static ListNode rest(ListNode h) {
      if (h == null || h.getNext() == null)
         return null;
      
      return new ListNode (h.getNext().getValue(), rest(h.getNext()));
   }     
     // returns the value of the first node, or null if the list is empty 
   public static Object first(ListNode head) {
      if (head != null)
         return head.getValue();
      else
         return null;
   } 
   
   // returns the value of the second node, or null if the list is empty or if there is only one node.  // hint:  second could call the first of rest. 
   public static Object second(ListNode head) {
      return first(rest(head));   
   }
   
   //returns a reference to the last node in the list, or null if the list is empty.
   public static ListNode pointerToLast(ListNode head) {
      if (head == null)
         return null;
      
      ListNode pointer = head;   
      while (pointer.getNext() != null)
         pointer = pointer.getNext();
      
      return pointer;
   }
   
   //returns a copy of the last node (not just its value!).  copyofLast can be recursive.  
   public static ListNode copyOfLast(ListNode head) {
      if (head == null)
         return head;
         
      return new ListNode(pointerToLast(head).getValue(), pointerToLast(head).getNext());
   }
   
   //returns a reference to a list whose first node's value is specified by the argument, and the 
   //first node's next links to the original list. 
   public static ListNode insertFirst(ListNode head, Object arg) {
      ListNode temp = new ListNode(arg, head);
      return temp;
   }
   
   //returns a reference to a list whose last node's value is specified by the argument, such 
   //that this last node has been appended to the original list and had its next is set to null 
   public static ListNode insertLast(ListNode head, Object arg) {
      ListNode last = pointerToLast(head);
      last.setNext(new ListNode(arg, null));
      return head;
   }
}

/*****************************************
 
 [computer, science, java, coffee, nonsense, boo, foo, hello]
 [computer, science, java, coffee, nonsense, boo, foo, hello]
 The head has a value "computer" at ListNode@15db9742
 The copy of head has a value of "computer" at ListNode@6d06d69c
 Copy the list: [computer, science, java, coffee, nonsense, boo, foo, hello]
 The rest of the list: [science, java, coffee, nonsense, boo, foo, hello]
 First of the rest = science
 Second of the rest = java
 Pointer to Last = hello at ListNode@7852e922
 Copy of Last =    hello at ListNode@4e25154f
 Insert what? p
 [p, science, java, coffee, nonsense, boo, foo, hello, p]
    
  **********************************************/