链表(单/双向 不带头 非循环)

一、什么是链表以及分类

1. 概念：逻辑上连续，物理上不连续，由一个个结点组成的数据结构
   
2. 链表分类：共有八种，单向or双向，带头的or不带头，循环or非循环排列组合

   • 单向 / 双向
     

   • 带头的 / 不带头的
     

   • 循环 / 非循环
     

3. 重点需要关注的两种链表：
   • 单向 + 不带头 + 非循环：做题常用
   • 双向 + 不带头 + 非循环：LinkedList底层是这个

二、模拟实现链表(单向不带头非循环)

2.1 细节解析

2.2 代码

public class MySingleList {
    static class ListNode {
        public int val;
        public ListNode next;

        public ListNode(int val) {
            this.val = val;
        }
    }

    public ListNode head;//永远指向我的头节点

    public void createList() {
        ListNode node1 = new ListNode(12);
        ListNode node2 = new ListNode(23);
        ListNode node3 = new ListNode(34);
        ListNode node4 = new ListNode(45);
        ListNode node5 = new ListNode(56);

        node1.next = node2;
        node2.next = node3;
        node3.next = node4;
        node4.next = node5;

        this.head = node1;
    }

    //遍历单链表
    public void show() {
        //这里不是定义了一个节点 这里只是一个引用
        ListNode cur = head;
        while (cur != null) {
            System.out.print(cur.val+" ");
            cur = cur.next;
        }
        System.out.println();
    }

    public void show(ListNode newHead) {
        //这里不是定义了一个节点 这里只是一个引用
        ListNode cur = newHead;
        while (cur != null) {
            System.out.print(cur.val+" ");
            cur = cur.next;
        }
        System.out.println();
    }

    //得到单链表的长度 --》 链表中节点的个数
    public int size(){
        int count = 0;
        ListNode cur = head;
        while (cur != null) {
            count++;
            cur = cur.next;
        }
        return count;
    }

    //查找是否包含关键字key是否在单链表当中
    public boolean contains(int key){
        ListNode cur = head;
        while (cur != null) {
            //如果val值 是引用类型  那么这里得用equals来进行比较！！！
            if(cur.val == key) {
                return true;
            }
            cur = cur.next;
        }
        return false;
    }

    //头插法
    public void addFirst(int data){
        ListNode node = new ListNode(data);
        node.next = head;
        head = node;
    }

    //尾插法
    public void addLast(int data){
        ListNode node = new ListNode(data);
        if(head == null) {
            head = node;
            return;
        }
        ListNode cur = head;
        while (cur.next != null) {
            cur = cur.next;
        }
        //cur 指向的节点就是尾巴节点
        cur.next = node;
    }

    //任意位置插入,第一个数据节点为0号下标
    public void addIndex(int index,int data){
        int len = size();
        //0、判断index位置的合法性
        if(index < 0 || index > len) {
            throw new IndexOutOfBounds("任意位置插入数据的时候，index位置不合法: "+index);
        }
        if(index == 0) {
            addFirst(data);
            return;
        }
        if(index == len) {
            addLast(data);
            return;
        }
        //1、先找到index-1位置的节点
        ListNode cur = findIndex(index);
        //2、进行插入
        ListNode node = new ListNode(data);
        node.next = cur.next;
        cur.next = node;
    }
    
    private ListNode findIndex(int index) {
        ListNode cur = head;
        while (index - 1 != 0) {
            cur = cur.next;
            index--;
        }
        return cur;//index-1位置的节点
    }
    //删除第一次出现关键字为key的节点
    public void remove(int key){
        if(head == null) {
            return;
        }
        if(head.val == key) {
            head = head.next;
            return;
        }
        ListNode prev = searchPrev(key);
        if(prev == null) {
            System.out.println("没有这个数据！");
            return;
        }
        ListNode del = prev.next;
        prev.next = del.next;
    }

    private ListNode searchPrev(int key) {
        ListNode prev = head;
        while (prev.next != null) {
            if(prev.next.val == key) {
                return prev;
            }else {
                prev = prev.next;
            }
        }
        return null;
    }

    //删除所有值为key的节点
    public void removeAllKey(int key){
        if(head == null) {
            return;
        }
        ListNode cur = head.next;
        ListNode prev = head;
        while (cur != null) {
            if(cur.val == key) {
                prev.next = cur.next;
                cur = cur.next;
            }else {
                prev = cur;
                cur = cur.next;
            }
        }
        if(head.val ==  key) {
            head = head.next;
        }
    }
    public void clear() {
        //this.head = null;
        while (head != null) {
            ListNode headNext = head.next;
            head.next = null;
            head = headNext;
        }
    }
}

三、模拟实现LinkedList(双向不带头非循环链表)

3.1 细节解析

3.2 代码

public class MyLinkedList {
    static class ListNode {
        public int val;
        public ListNode prev;
        public ListNode next;

        public ListNode(int val) {
            this.val = val;
        }
    }
    public ListNode head;
    public ListNode last;

    public int size(){
        int len = 0;
        ListNode cur = head;
        while (cur != null) {
            cur = cur.next;
            len++;
        }
        return len;
    }

    public void display(){
        ListNode cur = head;
        while (cur != null) {
            System.out.print(cur.val+" ");
            cur = cur.next;
        }
        System.out.println();
    }

    //查找是否包含关键字key是否在链表当中
    public boolean contains(int key){
        ListNode cur = head;
        while (cur != null) {
            if(cur.val == key) {
                return true;
            }
            cur = cur.next;
        }
        return false;
    }

    //头插法
    public void addFirst(int data){
        ListNode node = new ListNode(data);
        if(head == null) {
            head = node;
            last = node;
            return;
        }
        node.next = head;
        head.prev = node;
        head = node;
    }

    //尾插法
    public void addLast(int data){
        ListNode node = new ListNode(data);
        if(head == null) {
            head = node;
            last = node;
        }else {
            last.next = node;
            node.prev = last;
            last = node;//last = last.next;
        }
    }

    //任意位置插入,第一个数据节点为0号下标
    public void addIndex(int index,int data){
        int size = size();
        if(index < 0 || index > size) {
            throw new IndexOutOfBounds("双向链表index不合法！");
        }
        if(index == 0) {
            addFirst(data);
            return;
        }
        if(index == size) {
            addLast(data);
            return;
        }
        ListNode cur = head;
        while (index != 0) {
            cur = cur.next;
            index--;
        }
        ListNode node = new ListNode(data);
        node.next = cur;
        cur.prev.next = node;
        node.prev = cur.prev;
        cur.prev = node;
    }



    //删除第一次出现关键字为key的节点
    public void remove(int key){
        ListNode cur = head;
        while (cur != null) {
            if(cur.val == key) {
                //开始删除操作
                if(cur == head) {
                    //删除头节点
                    head = head.next;
                    //只有1个节点的时候
                    if(head != null) {
                        head.prev = null;
                    }else {
                        last = null;
                    }
                }else {
                    cur.prev.next = cur.next;
                    if(cur.next != null) {
                        cur.next.prev = cur.prev;
                    }else {
                        last = last.prev;
                    }
                }
                return;
            }else {
                cur = cur.next;
            }
        }
    }




    //删除所有值为key的节点
    public void removeAllKey(int key){
        ListNode cur = head;
        while (cur != null) {
            if(cur.val == key) {
                //进行删除操作
                if (cur == head) {
                    //删除头节点
                    head = head.next;
                    //只有1个节点的时候
                    if (head != null) {
                        head.prev = null;
                    }else {
                        last = null;
                    }
                } else {
                    cur.prev.next = cur.next;
                    if (cur.next != null) {
                        cur.next.prev = cur.prev;
                    } else {
                        last = last.prev;
                    }
                }
            }

            cur = cur.next;
        }
    }
    public void clear(){
        ListNode cur = head;
        while (cur != null) {
            ListNode curNext = cur.next;
            cur.prev = null;
            cur.next = null;
            //cur.val = null;
            cur = curNext;
        }
        head = null;
        last = null;
    }
}