题解 | #两两交换链表的节点#

import java.util.*;

/*
 * public class ListNode {
 *   int val;
 *   ListNode next = null;
 *   public ListNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param head ListNode类 
     * @return ListNode类
     */
    public ListNode swapLinkedPair (ListNode head) {
        // write code here
        
        if (null == head.next) {
            return head;
        }
        
        Queue<ListNode> q1 = new LinkedList<>();
        Queue<ListNode> q2 = new LinkedList<>();
        int index = 1;
        ListNode node = head;
        while (null != node) {
            if (index % 2 != 0) {
                q1.add(node);
            }
            else {
                q2.add(node);
            }
            node = node.next;
            index++;
        }
        head = q2.poll();
        node = head;
        while (!q1.isEmpty() && !q2.isEmpty()) {
            node.next = q1.poll();
            node = node.next;
            node.next = q2.poll();
            node = node.next;
        }
        while (!q1.isEmpty()) {
            node.next = q1.poll();
            node = node.next;
        }
        node.next = null;
        return head;
    }
}