451 - 两两交换链表中的节点

4.7

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public class Solution {
    /**
     * @param head a ListNode
     * @return a ListNode
     */
    public ListNode swapPairs(ListNode head) {
	     if(head == null || head.next == null){   
	    	 return head;
	     }
	     ListNode node1 = head;
	     ListNode node2 = head.next;
	     while(node1 != null && node2 != null){
	    	 int temp = node1.val;
	    	 node1.val = node2.val;
	    	 node2.val = temp;
	    	 node1 = node2.next;
	    	 if(node1 != null){
	    		 node2 = node1.next;
	    	 }
	    	 else{
	    		 return head;
	    	 }
	    	
	     }
		 return head;// Write your code here
	    }
}