单链表反转

来源：互联网发布：哈飞里程表算法编辑：程序博客网时间：2024/05/16 08:24

思路

（1）直接遍历链表，入栈，然后出栈重新构造链表
（2）递归，例如5交给4，4交给3…

代码

import java.util.*;//链表class Node {    int val;    Node next;    public Node(int val) {        this.val = val;    }}public class Main {    //递归处理后返回的头结点    static Node ans2;    //标记头结点    static Node marknode;    //1.使用栈    public static Node reverseOfList(Node pnode) {        Stack<Node> stack = new Stack<Node>();        Node temp = pnode;        while(temp != null) {            stack.push(temp);            temp = temp.next;        }        Node ans = stack.pop();        temp = ans;        while(!stack.empty()) {            temp.next = stack.pop();            temp = temp.next;        }        temp.next = null;        return ans;    }    //2.使用递归    public static Node reverseOfList2(Node pnode) {        //标记头结点，对其的next赋值null        marknode = pnode;        dfs(pnode);        return ans2;    }    public static Node dfs(Node pnode) {        Node rear;        if(pnode.next == null) {            ans2 = pnode;            rear = pnode;            return rear;        }        rear = dfs(pnode.next);        rear.next = pnode;        //如果此结点是原头结点，其next指向空        if(pnode == marknode)pnode.next = null;        return rear.next;    }    //测试    public static void main(String[] args) {        Node p = new Node(1);        p.next = new Node(2);        p.next.next = new Node(3);        p.next.next.next = new Node(4);        p.next.next.next.next = new Node(5);        Node ans = reverseOfList2(p);        Node temp = ans;        while(temp != null) {            System.out.print(temp.val+" ");            temp = temp.next;        }        System.out.println();    }}

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