算法學習之基礎(揹包 列隊 棧) 習題1.3.33泛型雙向隊列

前幾天寫的。。

  1 package gh;
  2 
  3 import java.util.Iterator;
  4 
  5 /**
  6  * 泛型雙向隊列（雙向鏈表實現）
  7  * @author ganhang
  8  *
  9  */
 10 public class Deque<T> implements Iterable<T> {
 11     private Node first;
 12     private Node last;
 13     private int n=0;
 14     public Deque(){
 15         
 16     }
 17     //從左邊加入
 18     public void pushLeft(T item) {
 19         if (first == null) {
 20             first=new Node(item);    
 21             last=first;
 22         }else{
 23             Node oldfirst = first;
 24             first=new Node(item);
 25             first.next=oldfirst;
 26             oldfirst.pre=first;
 27         }
 28         n++;
 29     }
 30     //從右邊加入
 31     public void pushRight(T item){
 32         if(last==null){
 33             last=new Node(item);
 34             first=last;
 35         }else{
 36             Node oldlast=last;
 37             last=new Node(item);
 38             oldlast.next=last;
 39             last.pre=oldlast;
 40         }
 41         n++;
 42     }
 43     //從左邊彈出一個元素
 44     public T popLeft() {
 45         if (first != null) {
 46             T item = first.item;
 47             first = first.next;
 48             n--;
 49             return item;
 50         }
 51         return null;
 52     }
 53     //從右邊彈出一個元素
 54     public T popRight(){
 55         if(last!=null){
 56             T item=last.item;
 57             last=last.pre;
 58             n--;
 59             return item;
 60         }
 61         return null;
 62     }
 63     public int size(){
 64         return n;
 65     }
 66     public boolean isEmpty(){
 67         return n==0;
 68     }
 69     private class Node{
 70         private T item;
 71         private Node pre;
 72         private Node next;
 73         public Node(T item){
 74             this.item=item;
 75         }
 76     }
 77     @Override
 78     public Iterator<T> iterator() {
 79         // TODO Auto-generated method stub
 80         return new DequeIterator();
 81     }
 82     private class DequeIterator implements Iterator<T>{
 83         private Node current=first;
 84         @Override
 85         public boolean hasNext() {
 86             // TODO Auto-generated method stub
 87             return current!=null;
 88         }
 89 
 90         @Override
 91         public T next() {
 92             // TODO Auto-generated method stub
 93             T item=current.item;
 94             current=current.next;
 95             return item;
 96         }
 97 
 98         @Override
 99         public void remove() {
100             // TODO Auto-generated method stub
101             
102         }
103         
104     }
105 
106 }

測試

Deque<String> d=new Deque<String>();
        d.pushLeft("a");
        d.pushLeft("b");
        d.pushLeft("c");
        d.pushLeft("d");
        d.pushRight("1");
        d.pushRight("2");
        d.pushRight("3");
        d.pushRight("4");
        while(!d.isEmpty()){
            System.out.println(d.popRight());
        }
        System.out.println("-----------");
        for(String s:d)
        System.out.println(s);

輸出

4
3
2
1
a
b
c
d
-----------
d
c
b
a
1
2
3
4