LeetCode 24. Swap Nodes in Pairs

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public class Solution {
    public ListNode swapPairs(ListNode head) {
        
        if(head == null || head.next == null)
            return head;
        
        ListNode p1 = head;
        ListNode p2 = head.next;
        ListNode result = p2;
        ListNode temp = null;
        while(p1 != null && p2 != null)
        {
            p1.next = p2.next;
            p2.next = p1;
            
            if(temp != null)
                temp.next = p2;
            temp = p1;
            if(p1.next != null && p1.next.next !=null)
            {
                p1 = p1.next;
                p2 = p1.next;
            }
            else
                break;
            
        }
        return result;
    }
}

 

 

https://discuss.leetcode.com/topic/4351/my-accepted-java-code-used-recursion/5

public class Solution {
    public ListNode swapPairs(ListNode head) {
        if ((head == null)||(head.next == null))
            return head;
        ListNode n = head.next;
        head.next = swapPairs(head.next.next);
        n.next = head;
        return n;
    }
}