交换相邻节点

1

class ListNode {
    int val;
    ListNode next;

    ListNode(int val) {
        this.val = val;
        this.next = null;
    }
}

public class SwapNodes {

    // 方法：交换相邻节点
    public static ListNode swapPairs(ListNode head) {
        // 如果链表为空或只有一个节点，则直接返回
        if (head == null || head.next == null) {
            return head;
        }

        // 创建一个虚拟节点作为新的头节点的前驱
        ListNode dummy = new ListNode(0);
        dummy.next = head;
        ListNode current = dummy;

        // 迭代交换相邻节点
        while (current.next != null && current.next.next != null) {
            // 初始化要交换的两个节点
            ListNode first = current.next;
            ListNode second = current.next.next;

            // 交换节点
            first.next = second.next;
            second.next = first;
            current.next = second;

            // 移动指针到下一个要交换的节点位置
            current = first;
        }

        // 返回新的头节点
        return dummy.next;
    }

    // 辅助方法：打印链表
    public static void printList(ListNode head) {
        ListNode current = head;
        while (current != null) {
            System.out.print(current.val + " ");
            current = current.next;
        }
        System.out.println();
    }

    public static void main(String[] args) {
        // 创建链表 1 -> 2 -> 3 -> 4
        ListNode head = new ListNode(1);
        head.next = new ListNode(2);
        head.next.next = new ListNode(3);
        head.next.next.next = new ListNode(4);

        System.out.println("原始链表：");
        printList(head);

        // 交换相邻节点
        head = swapPairs(head);

        System.out.println("交换相邻节点后的链表：");
        printList(head);
    }
}