算法学习之基础(背包 列队 栈) 习题1.3.33泛型双向队列

前几天写的。。

package gh;

import java.util.Iterator;

/**
 * 泛型双向队列（双向链表实现）
 * @author ganhang
 *
 */
public class Deque<T> implements Iterable<T> {
    private Node first;
    private Node last;
    private int n=0;
    public Deque(){
        
    }
    //从左边加入
    public void pushLeft(T item) {
        if (first == null) {
            first=new Node(item);    
            last=first;
        }else{
            Node oldfirst = first;
            first=new Node(item);
            first.next=oldfirst;
            oldfirst.pre=first;
        }
        n++;
    }
    //从右边加入
    public void pushRight(T item){
        if(last==null){
            last=new Node(item);
            first=last;
        }else{
            Node oldlast=last;
            last=new Node(item);
            oldlast.next=last;
            last.pre=oldlast;
        }
        n++;
    }
    //从左边弹出一个元素
    public T popLeft() {
        if (first != null) {
            T item = first.item;
            first = first.next;
            n--;
            return item;
        }
        return null;
    }
    //从右边弹出一个元素
    public T popRight(){
        if(last!=null){
            T item=last.item;
            last=last.pre;
            n--;
            return item;
        }
        return null;
    }
    public int size(){
        return n;
    }
    public boolean isEmpty(){
        return n==0;
    }
    private class Node{
        private T item;
        private Node pre;
        private Node next;
        public Node(T item){
            this.item=item;
        }
    }
    @Override
    public Iterator<T> iterator() {
        // TODO Auto-generated method stub
        return new DequeIterator();
    }
    private class DequeIterator implements Iterator<T>{
        private Node current=first;
        @Override
        public boolean hasNext() {
            // TODO Auto-generated method stub
            return current!=null;
        }

        @Override
        public T next() {
            // TODO Auto-generated method stub
            T item=current.item;
            current=current.next;
            return item;
        }

        @Override
        public void remove() {
            // TODO Auto-generated method stub
            
        }
        
    }

}

测试

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);

输出

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