链表（上）

链表（上）

链表（Linked list）是一种常见的基础数据结构，是一种线性表，但是并不会按线性的顺序存储数据，而是在每一个节点里存到下一个节点的指针(Pointer)。

相对于数组来讲，链表不需要预先知道数据的大小，它更灵活，可以充分利用计算机的内存空间。缺点是不能像数组一样随机读取数据，而且空间花销也比较大。常见链表有以下几种：

单向链表

单链表（即单向链表）是最简单的链表结构。一个单链表的节点 (Node) 分为两个部分，第一个部分 (data) 是节点本身的数据，另一个部分 (next) 是指向下一个节点的指针。

来个代码看看：

package mylink;

public class MyLink<T> {  
    private class ListNode{  
        private T val;  
        private ListNode next;  //默认为 null

        ListNode(T val){  
            this.val = val;  
        }  
    }  

    private ListNode first = null;  

    public void insertFirst(T val){   //头插法
        ListNode data = new ListNode(val);  
        data.next = first;  
        first = data;  
    }  

    public Object deleteFirst() throws Exception{  
        if(first == null)  
            throw new Exception("empty!");  
        ListNode temp = first;  
        first = first.next;  
        return temp.val;  
    }  

    public Object find(Object val) throws Exception{  
        if(first == null)  
            throw new Exception("LinkedList is empty!");  
        ListNode cur = first;  
        while(cur != null){  
            if(cur.val.equals(val)){  
                return cur.val;  
            }  
            cur = cur.next;  
        }  
        return null;  
    }  

    public void remove(Object val) throws Exception{  
        if(first == null)  
            throw new Exception("LinkedList is empty!");  
        if(first.val.equals(val)){  
            first = first.next;  
        }else{  
            ListNode pre = first;  
            ListNode cur = first.next;  
            while(cur != null){  
                if(cur.val.equals(val)){  
                    pre.next = cur.next;  
                }  
                pre = cur;  
                cur = cur.next;  
            }  
        }  
    }  

    public boolean isEmpty(){  
        return (first == null);  
    }  

    public void display(){  
        if(first == null)  
            System.out.println("empty");  
        ListNode cur = first;  
        while(cur != null){  
            System.out.print(cur.val.toString() + " -> ");  
            cur = cur.next;  
        }  
        System.out.print("\n");  
    }  

    public static void main(String[] args) throws Exception {  
        MyLink<Integer> list = new MyLink<Integer>();  
        list.insertFirst(4);  
        list.insertFirst(3);  
        list.insertFirst(2);  
        list.insertFirst(1);  
        list.display();  
        list.deleteFirst();  
        list.display();  
        list.remove(3);  
        list.display();  
        System.out.println(list.find(1));  
        System.out.println(list.find(4));  
    }  
}  

运行结果截图：

其实就是一个链表类里面有一个节点类，节点类的核心代码如下：

public class ListNode {
    int val;
    ListNode next;
    ListNode(int x) { val = x; }
 }

双端链表

就是有头有尾的单向链表，代码如下：

package mylink;

public class MyLink<T> {  
    private class ListNode{  
        private T val;  
        private ListNode next;  

        ListNode(T val){  
            this.val = val;  
        }  
    }  

    private ListNode first = null;  
    private ListNode last = null;  

    public void insertFirst(T val){  
        ListNode data = new ListNode(val);  
        if(first == null)  
            last = data;  
        data.next = first;  
        first = data;  
    }  

    public void insertLast(T val){  
        ListNode data = new ListNode(val);  
        if(first == null){  
            first = data;  
        }else{  
            last.next = data;  

        }  
        last = data;  
    }  

    public Object deleteFirst() throws Exception{  
          if(first == null)  
             throw new Exception("empty");  
          ListNode temp = first;  
          if(first.next == null)  
             last = null;  
          first = first.next;  
          return temp.val;  
   }     

    public void deleteLast() throws Exception{  
        if(first == null)  
            throw new Exception("empty");  
        if(first.next == null){  
            first = null;  
            last = null;  
        }else{  
            ListNode temp = first;  
            while(temp.next != null){  
                if(temp.next == last){  
                    last = temp;  
                    last.next = null;  
                    break;  
                }  
                temp = temp.next;  
            }  
        }  
    }  

    public void display(){  
        if(first == null)  
            System.out.println("empty");  
        ListNode cur = first;  
        while(cur != null){  
            System.out.print(cur.val.toString() + " -> ");  
            cur = cur.next;  
        }  
        System.out.print("\n");  
    }  

    public static void main(String[] args) throws Exception {  
        MyLink<Integer> list = new MyLink<Integer>();  
        list.insertFirst(2);  
        list.insertFirst(1);  
        list.display();  
        list.insertLast(3);  
        list.display();  
        list.deleteFirst();  
        list.display();  
        list.deleteLast();  
        list.display();  
    }  
}  

运行结果截图：

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