數據結構 ——鏈表（虛擬頭結點）

public class LinkedList2<E> {

    //另外一種思路
    // 內存空間不是連續的 即物理空間不是連續的 邏輯空間依賴着next指向是連續的
    private class Node{
        public E e;
        public Node next;

        public Node(E e, Node next){
            this.e = e;
            this.next = next;
        }

        public Node(E e){
            this(e,null);
        }

        public Node(){
            this(null,null);
        }

        @Override
        public String toString(){
            return e.toString();
        }
    }

    private Node dummyHead;  //虛擬頭結點,在頭結點前面創建一個節點
    private int size;

    public LinkedList2(){
        dummyHead = new Node();
        size = 0;
    }

    //獲取鏈表中元素個數
    public int getSize(){
        return size;
    }

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

    public void addFirst(E e){
        add(0,e);
    }

    //在指定位置添加結點
    // 由於並不常見 所以我們定義head 為 第 0 個元素
    public void add(int index, E e){
        if (index < 0 || index > size){
            throw new IllegalArgumentException("指定位置越界");
        }
        if(index == 0){
            addFirst(e);
        }else{
            Node pre = dummyHead;
            for (int i = 0 ; i < index ; i++){
                pre = pre.next;
            }

            /*Node c = new Node(e);
            c.next = pre.next;
            pre.next = c;*/
            pre.next = new Node(e,pre.next);
            size--;
        }
    }
    public void addLast(E e){
        add(size,e);
    }

    public E get(int index ){
        if (index < 0 || index > size){
            throw new IllegalArgumentException("越界");
        }

        Node cur = dummyHead.next;
        for (int i = 0 ; i < index ; i++) {
            cur = cur.next;

        }
        return cur.e;
    }
    public E getFirst(){
        return get(0);
    }
    public E getLast(){
        return get(size);
    }

    // 查詢是否存在元素e
    public boolean contains(E e) {
        Node cur = dummyHead.next;
        for (int i = 0; i < size; i++) {

            if (cur.e == e) {
                return true;
            }
            cur = cur.next;
        }
         return false;
    }

    public E remove(int index){
        if (index < 0 || index > size){
            throw new IllegalArgumentException("下標越界");
        }
        Node cur = dummyHead;
        for (int i =0 ; i < index ; i++){
            cur = cur.next;
        }
        Node t = new Node();
        cur.next = t;
        cur.next = t.next;
        t.next = null;
        size --;
        return t.e;

    }

    public E removeFirst(){
        return remove(0);
    }

    public E removeLast(){
        return remove(size);
    }

}

 

 

在head 結點的前面的創建虛擬頭結點。  為了使修改刪除 ，讓head結點和普通結點一視同仁