[数据结构]之链表

1. 链表与数组的比较：

2. 链表的实现：

package com.ytuan.linkedList;

public class LinkedList<E> {

//    private Node head;
    private Node dummyHead;
    private int size;

    public LinkedList() {
//        head = new Node();
        dummyHead = new Node();
        size = 0;
    }

    public int getSize() {
        return size;
    }

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

    /**
     * 找到需要插入索引的前一个节点是关键
     * 
     * @param index
     * @param e
     */
    public void add(int index, E e) {

        if (index < 0 || index > size)
            throw new IllegalArgumentException("add faild! index illegalment");

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

//            Node newNode = new Node(e);
//            newNode.next = pre.next;
//            pre.next = newNode;

        pre.next = new Node(e, pre.next);

        size++;
    }

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

    public void addLast(E e) {
        add(size, e);
    }

    public E get(int index) {

        if (index < 0 || index >= size)
            throw new IllegalArgumentException("add faild! index illegalment");

        Node cur = dummyHead.next;
        for (int i = 0; i < index; i++) { // 共需要next index- 1 次
            cur = cur.next;
        }

        return cur.e;
    }

    public E getFirst() {
        return get(0);
    }

    public E getLast() {
        return get(size - 1);
    }

    public void set(int index, E e) {

        if (index < 0 || index >= size)
            throw new IllegalArgumentException("add faild! index illegalment");

        Node cur = dummyHead.next;

        for (int i = 0; i < index; i++)
            cur = cur.next;
        cur.e = e;
    }

    public boolean contains(E e) {

        Node cur = dummyHead.next;
        while (cur!= null) {
            if (cur.e.equals(e))
                return true;
            cur = cur.next;
        }

        return false;
    }

    @Override
    public String toString() {

        StringBuffer res = new StringBuffer();

//        res.append(String.format("LinkedList  size = %d 
", size));

        Node pre = dummyHead;
        while (pre.next != null) {
            res.append(pre.next.e + " ->");
            pre = pre.next;
        }

        res.append("null");

        return res.toString();
    }

    public E remove(int index) {

        if (index < 0 || index >= size)
            throw new IllegalArgumentException("add faild! index illegalment");

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

        Node delNode = pre.next;
        E res = delNode.e;

        pre.next = delNode.next;

        delNode.next = null;

        size--;
        return res;

    }

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

    public E removeLast() {
        return remove(size - 1);
    }

    private class Node {
        E e;
        Node next;

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

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

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

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

    }
}

 

 

3. 使用链表实现的栈：

package com.ytuan.stack;

import com.ytuan.linkedList.LinkedList;

public class LinkedListStack<E> implements Stack<E> {

    private LinkedList<E> list;

    public LinkedListStack() {
        // TODO Auto-generated constructor stub
        list = new LinkedList<>();
    }

    @Override
    public void push(E e) {
        // TODO Auto-generated method stub
        list.addLast(e);

    }

    @Override
    public E pop() {
        // TODO Auto-generated method stub
        return list.removeFirst();
    }

    @Override
    public E peek() {
        // TODO Auto-generated method stub
        return list.getFirst();
    }

    @Override
    public int getSize() {
        // TODO Auto-generated method stub
        return list.getSize();
    }

    @Override
    public boolean isEmpty() {
        // TODO Auto-generated method stub
        return list.isEmpty();
    }

    @Override
    public String toString() {
        // TODO Auto-generated method stub
        StringBuffer res = new StringBuffer();
        
        res.append("Stack : top  ");
        
        res.append(list);
        return res.toString();
    }
    
    

}

 4. 使用链表实现队列

代码实现：

package com.ytuan.queue;

public class LinkedListQueue<E> implements Queue<E> {

    private Node head;
    private Node tail;
    private int size;

    public LinkedListQueue() {
        this.head = null;
        this.tail = null;
        this.size = 0;
    }

    @Override
    public void enqueue(E e) {

        if (tail == null) { // 此时链表为空
            tail = new Node(e);
            head = tail;
        } else {
            tail.next = new Node(e);
            tail = tail.next;
        }

        size++;
    }

    @Override
    public E dequeue() {

        if (isEmpty())
            throw new IllegalArgumentException("no element to dequeue");

        Node delNode = head;
        head = head.next;

        if (head == null)
            tail = null;

        delNode.next = null;
        size--;
        return delNode.e;
    }

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

    @Override
    public int getSize() {
        return size;
    }

    @Override
    public E getFront() {
        if (isEmpty())
            throw new IllegalArgumentException("queue is empty");
        return head.e;
    }

    @Override
    public String toString() {

        StringBuffer res = new StringBuffer();

        res.append("Queue  front ->");

        Node cur = head;
        for (int i = 0; i < size; i++) {
            if (cur != null)
                res.append(cur.e + "->");
            if (cur.next != null)
                cur = cur.next;
        }

        res.append("tail");

        return res.toString();
    }

    private class Node {

        private E e;

        private Node next;

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

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

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

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

}

 5. 链表实战

leetcode 230 号问题 ：https://leetcode-cn.com/problems/remove-linked-list-elements/

 无头节点解答：

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode removeElements(ListNode head, int val) {

        // head 就是目标元素
        while (head != null && head.val == val) {
            head = head.next;
        }

        // 没有元素了
        if (head == null)
            return head;

        ListNode pre = head;
        while (pre.next != null) {
            if (pre.next.val == val) {
                pre.next = pre.next.next;
            } else {
                pre = pre.next;
            }
        }

        return head;
    }
}

带头节点解答：

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {

    ListNode dummyNode = new ListNode(0);

    public ListNode removeElements(ListNode head, int val) {

        if (head == null)
            return head;
        
        dummyNode.next = head;

        ListNode pre = dummyNode;
        while (pre.next != null) {
            if (pre.next.val == val)
                pre.next = pre.next.next;
            else
                pre = pre.next;
        }

        return dummyNode.next;
    }
}