hw3

smoosh相对来说比较复杂一些，尤其是最后一个数字向后比较的时候，很容易就丢了一个数，作业上说是用了14行码，我正好也是14行。后面squish开始忘记了比较要用equals不能用==，也是卡了半天，不好好审题。后面加了一些testcode检验这三个method。

import java.lang.reflect.Array;

/* SList.java */

/**
 *  The SList class is a singly-linked implementation of the linked list
 *  abstraction.  SLists are mutable data structures, which can grow at either
 *  end.
 *
 *  @author Kathy Yelick and Jonathan Shewchuk
 **/

public class SList {

  private SListNode head;
  private int size;


  /**
   *  SList() constructs an empty list.
   **/

  public SList() {
    size = 0;
    head = null;
  }

  /**
   *  isEmpty() indicates whether the list is empty.
   *  @return true if the list is empty, false otherwise.
   **/

  public boolean isEmpty() {
    return size == 0;
  }

  /**
   *  length() returns the length of this list.
   *  @return the length of this list.
   **/

  public int length() {
    return size;
  }

  /**
   *  insertFront() inserts item "obj" at the beginning of this list.
   *  @param obj the item to be inserted.
   **/

  public void insertFront(Object obj) {
    head = new SListNode(obj, head);
    size++;
  }

  /**
   *  insertEnd() inserts item "obj" at the end of this list.
   *  @param obj the item to be inserted.
   **/

  public void insertEnd(Object obj) {
    if (head == null) {
      head = new SListNode(obj);
    } else {
      SListNode node = head;
      while (node.next != null) {
        node = node.next;
      }
      node.next = new SListNode(obj);
    }
    size++;
  }

  /**
   *  nth() returns the item at the specified position.  If position < 1 or
   *  position > this.length(), null is returned.  Otherwise, the item at
   *  position "position" is returned.  The list does not change.
   *  @param position the desired position, from 1 to length(), in the list.
   *  @return the item at the given position in the list.
   **/

  public Object nth(int position) {
    SListNode currentNode;

    if ((position < 1) || (head == null)) {
      return null;
    } else {
      currentNode = head;
      while (position > 1) {
        currentNode = currentNode.next;
        if (currentNode == null) {
          return null;
        }
        position--;
      }
      return currentNode.item;
    }
  }
  /**
   *  smoosh() takes an array of ints.  On completion the array contains
   *  the same numbers, but wherever the array had two or more consecutive
   *  duplicate numbers, they are replaced by one copy of the number.  Hence,
   *  after smoosh() is done, no two consecutive numbers in the array are the
  * same. *
   *  Any unused elements at the end of the array are set to -1.
   *
   *  For example, if the input array is [ 0 0 0 0 1 1 0 0 0 3 3 3 1 1 0 ],
   *  it reads [ 0 1 0 3 1 0 -1 -1 -1 -1 -1 -1 -1 -1 -1 ] after smoosh()
   *  completes.
   *
   *  @param ints the input array.
   **/
  
  public static void smoosh(int[] ints) {
      int k=0;
     int lengthOriginal=Array.getLength(ints);
      int lengthOf=lengthOriginal;
     for(int i=0;i<lengthOf;i++){
         if(ints[i]==ints[i+1]){
             for(int j=i+1;j<lengthOf;j++){
                 ints[j-1]=ints[j];             
         }
         lengthOf--;
         k++;
         if(i!=lengthOf-1)i--;}
     }
     for(int x=lengthOriginal-k;x<lengthOriginal;x++){
         ints[x]=-1;
     }

      
      // Fill in your solution here.  (Ours is fourteen lines long, not counting
      // blank lines or lines already present in this file.)
  }
  /**
   *  squish() takes this list and, wherever two or more consecutive items are
   *  equals(), it removes duplicate nodes so that only one consecutive copy
   *  remains.  Hence, no two consecutive items in this list are equals() upon
   *  completion of the procedure.
   *
   *  After squish() executes, the list may well be shorter than when squish()
   *  began.  No extra items are added to make up for those removed.
   *
   *  For example, if the input list is [ 0 0 0 0 1 1 0 0 0 3 3 3 1 1 0 ], the
   *  output list is [ 0 1 0 3 1 0 ].
   *
   *  IMPORTANT:  Be sure you use the equals() method, and not the "=="
   *  operator, to compare items.
   **/

  public void squish() {
    SListNode a=head;
    while(a!=null){
    if(a.next!=null){
        if(a.item.equals(a.next.item)){
          a.next=a.next.next;
          size--;
    }else  a=a.next;
    
    }else a=a.next;
}}
  /**
   *  twin() takes this list and doubles its length by replacing each node
   *  with two consecutive nodes referencing the same item.
   *
   *  For example, if the input list is [ 3 7 4 2 2 ], the
   *  output list is [ 3 3 7 7 4 4 2 2 2 2 ].
   *
   *  IMPORTANT:  Do not try to make new copies of the items themselves.
   *  Make new SListNodes, but just copy the references to the items.
   **/

  public void twin() {
    SListNode original=head;
    SListNode copy;
    while(original!=null){
        copy=new SListNode(original.item,original.next);
        original.next=copy;
        original=copy.next;
        
    }// Fill in your solution here.  (Ours is seven lines long.)
  }

  /**
   *  toString() converts the list to a String.
   *  @return a String representation of the list.
   **/

  public String toString() {
    int i;
    Object obj;
    String result = "[  ";

    SListNode cur = head;

    while (cur != null) {
      obj = cur.item;
      result = result + obj.toString() + "  ";
      cur = cur.next;
    }
    result = result + "]";
    return result;
  }


  /**
   *  main() runs test cases on the SList class.  Prints summary
   *  information on basic operations and halts with an error (and a stack
   *  trace) if any of the tests fail.
   **/

  public static void main (String[] args) {
    int[] myArray={3,7,7,7,7,4,4,2,2,2,2,1};
    smoosh(myArray);
    testEmpty();
    testAfterInsertFront();
    testAfterInsertEnd();
    testsmoosh();
    testsquish();
    testtwin();
    
  }
  private static void testsmoosh(){
      int[] testInt={1,2,2,2,3,3,3,5,5,5};
      System.out.println("Here is the original Array: ");
            for(int i=0;i<10;i++){
              System.out.print(testInt[i]);
            } 
             System.out.println();
             System.out.println("Here is the Array after smoosh method: ");
                smoosh(testInt);
             for(int i=0;i<10;i++){
                  System.out.print(testInt[i]);
                } 
  }
  private static void testsquish(){
      SList testList1=new SList();
     testList1.insertFront(1);
     testList1.insertFront(1);
     testList1.insertFront(2);
     testList1.insertFront(2);
     testList1.insertFront(3);
     testList1.insertFront(3);
     testList1.insertFront(3);
     System.out.println();
     System.out.println("Here is a list of original construction: "
                   + testList1.toString());
     testList1.squish();
        System.out.println("Here is a list of after squish method: "
                   + testList1.toString());
  }
  private static void testtwin(){
      SList testList2=new SList();
      testList2.insertFront(1);
      testList2.insertFront(2);
      testList2.insertFront(3);
      testList2.insertFront(4);
      testList2.insertFront(5);
      testList2.insertFront(5);
      System.out.println();
      System.out.println("Here is a list of original construction: "
                   + testList2.toString());
      testList2.twin();
          System.out.println("Here is a list after twin method: "
               + testList2.toString());
  }
    
  /**
   *  testEmpty() tests toString(), isEmpty(), length(), insertFront(), and
   *  insertEnd() on an empty list.  Prints summary information of the tests
   *  and halts the program if errors are detected.
   **/

  private static void testEmpty() {
    SList lst1 = new SList();
    SList lst2 = new SList();
    System.out.println();
    System.out.println("Here is a list after construction: "
               + lst1.toString());
    TestHelper.verify(lst1.toString().equals("[  ]"),
              "toString on newly constructed list failed");

    System.out.println("isEmpty() should be true. It is: " +
               lst1.isEmpty());
    TestHelper.verify(lst1.isEmpty() == true,
              "isEmpty() on newly constructed list failed");    

    System.out.println("length() should be 0. It is: " +
               lst1.length());
    TestHelper.verify(lst1.length() == 0, 
              "length on newly constructed list failed");    
    lst1.insertFront(new Integer(3));
    System.out.println("Here is a list after insertFront(3) to an empty list: "
               + lst1.toString());
    TestHelper.verify(lst1.toString().equals("[  3  ]"),
              "InsertFront on empty list failed");
    lst2.insertEnd(new Integer(5));
    System.out.println("Here is a list after insertEnd(5) on an empty list: "
               + lst2.toString());
    TestHelper.verify(lst2.toString().equals("[  5  ]"),
              "insertEnd on empty list failed");
  }

  /**
   *  testAfterInsertFront() tests toString(), isEmpty(), length(),
   *  insertFront(), and insertEnd() after insertFront().  Prints summary
   *  information of the tests and halts the program if errors are detected.
   **/

  private static void testAfterInsertFront() {
    SList lst1 = new SList();
    lst1.insertFront(new Integer(3));
    lst1.insertFront(new Integer(2));
    lst1.insertFront(new Integer(1));
    System.out.println();
    System.out.println("Here is a list after insertFront 3, 2, 1: "
               + lst1.toString());
    System.out.println("Here is a list after insertFront 3, 2, 1: "
               + lst1.toString());
    TestHelper.verify(lst1.toString().equals("[  1  2  3  ]"),
              "InsertFronts on non-empty list failed");
    System.out.println("isEmpty() should be false. It is: " +
               lst1.isEmpty());
    TestHelper.verify(lst1.isEmpty() == false,
              "isEmpty() after insertFront failed");    
    System.out.println("length() should be 3. It is: " +
               lst1.length());
    TestHelper.verify(lst1.length() == 3, 
              "length() after insertFront failed");
    lst1.insertEnd(new Integer(4));
    System.out.println("Here is the same list after insertEnd(4): "
               + lst1.toString());
    TestHelper.verify(lst1.toString().equals("[  1  2  3  4  ]"),
              "insertEnd on non-empty list failed");
  }
    
  /**
   *  testAfterInsertEnd() tests toString(), isEmpty(), length(),
   *  insertFront(), and insertEnd() after insertEnd().  Prints summary
   *  information of the tests and halts the program if errors are detected.
   **/

  private static void testAfterInsertEnd() {
    SList lst1 = new SList();
    lst1.insertEnd(new Integer(6));
    lst1.insertEnd(new Integer(7));
    System.out.println();
    System.out.println("Here is a list after insertEnd 6, 7: "
               + lst1.toString());
    System.out.println("isEmpty() should be false. It is: " +
               lst1.isEmpty());
    TestHelper.verify(lst1.isEmpty() == false,
              "isEmpty() after insertEnd failed");    
    System.out.println("length() should be 2. It is: " +
               lst1.length());
    TestHelper.verify(lst1.length() == 2, 
              "length() after insertEndfailed");
    lst1.insertFront(new Integer(5));
    System.out.println("Here is the same list after insertFront(5): "
               + lst1.toString());
    TestHelper.verify(lst1.toString().equals("[  5  6  7  ]"),
              "insertFront after insertEnd failed");
  }
}

运行结果：