【leetcode-两两交换链表中的节点】

迭代法

  public ListNode swapPairs(ListNode head) {
        if(head==null || head.next==null){
            return head;
        }
        ListNode result = new ListNode(0);
        result.next=head;
        ListNode curr = result;
        while(curr.next !=null && curr.next.next!=null){
            ListNode next = head.next;
                    ListNode tmp = next.next;

                    curr.next=next;
                    next.next=head;
                    head.next=tmp;

                    curr=head;
                    head=head.next;
        }
        return result.next;
    }

递归法

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