链表逆序、逆转

链表分为单链表、双链表，此次讨论单链表的情况。之前有思考链表如何逆转，直到看了HashMap 1.7的resize操作，才发现原来逆转有这样简洁的写法(1.8虽然没有逆转，但实现也很经典，感兴趣可以自己研究)。特此记录分享下：

要实现的效果如下：

节点定义

package com.syj.test.linkedtest;

import lombok.Data;

/**
 * Created by syj on 2018/2/8.
 */
@Data
public class Node {

    private String val;

    private Node next;

    Node(){}

    Node(String val) {
        this.val = val;
    }

    Node(String val, Node next) {
        this.val = val;
        this.next = next;
    }

}

逆转逻辑

package com.syj.test.linkedtest;

/**
 * Created by syj on 2018/2/8.
 */
public class LinkReverse {

    public static void main(String[] args) {
        Node node1 = new Node("node1");
        Node node2 = new Node("node2");
        Node node3 = new Node("node3");
        Node node4 = new Node("node4");

        node1.setNext(node2);
        node2.setNext(node3);
        node3.setNext(node4);

        System.out.println("before:" + node1);
        Node reverseNode = reverse(node1);
        System.out.println("after:" + reverseNode);

    }

    private static Node reverse(Node node) {
        Node head = null;
        Node next = null;
        do {
            next = node.getNext();

            //将当前元素的下一个元素，指向当前链表的头部
            node.setNext(head);
            //将头部指向当前元素
            head = node;
        } while ((node = next) != null);

        return head;
    }
}