题目：swap nodes in pairs

<span style="font-size:18px;">/**

 * LeetCode Swap Nodes in Pairs

 * 题目：输入一个链表，要求将链表每相邻的两个节点交换位置后输出

 * 思路：遍历一遍就可以，时间复杂度O(n)

 * Definition for singly-linked list.

 * public class ListNode {

 *     int val;

 *     ListNode next;

 *     ListNode(int x) {

 *         val = x;

 *         next = null;

 *     }

 * }

 */

package javaTrain; 

public class Train12 {

	public ListNode swapPairs(ListNode head) {

		if(head == null || head.next == null) return null;

        ListNode pNode;

        pNode = head;

        while(pNode != null && pNode.next != null){

        	int temp;

        	temp = pNode.val;

        	pNode.val = pNode.next.val;

        	pNode.next.val = temp;

        	pNode = pNode.next.next;

        }

        return head;

    }

}

</span>