package com.zmz.algorithm.listnode;

/**
 * @author 张明泽
 * Create by 2022/5/28 17:28
 * 两两交换链表中的节点
 * LeetCode-24
 */
public class SwapPairNode {
    public static void main(String[] args) {
        ListNode head = new ListNode(1);
        ListNode node2 = new ListNode(2);
        ListNode node3 = new ListNode(3);
        ListNode node4 = new ListNode(4);
        head.next = node2;
        node2.next = node3;
        node3.next = node4;
        ListNode result = swap(head);
        traverse(result);
    }

    /**
     * 虚拟节点
     * 画图,不画图看不懂指针的走向
     * 为什么要存节点? 只要链表的方向发生改变了如果还想使用就得提前存起来
     */
    public static ListNode swap(ListNode listNode) {
        ListNode header = new ListNode(-1);
        header.next = listNode;
        ListNode head = header;
        while (head.next != null && head.next.next != null) {
            ListNode temp = head.next;
            ListNode temp2 = head.next.next.next;
            head.next = head.next.next;
            head.next.next = temp;
            head.next.next.next = temp2;
            head = head.next.next;
        }
        return header.next;
    }
    public static class ListNode {
        int val;
        ListNode next;
        ListNode() {}
        ListNode(int val) { this.val = val; }
        ListNode(int val, ListNode next) {
            this.val = val;
            this.next = next;
        }
    }
    public static void traverse(ListNode listNode) {
        while (listNode != null) {
            System.out.println(listNode.val);
            listNode = listNode.next;
        }
    }
}