合并两个有序链表

题目描述：

将两个有序链表合并为一个新的有序链表并返回。新链表是通过拼接给定的两个链表的所有节点组成的。 

示例：

输入：1->2->4, 1->3->4
输出：1->1->2->3->4->4

class ListNode:
    def __init__(self, x):
        self.val = x
        self.next = None

class Solution:
   def mergeTwoLists(self, l1, l2):
        root = l = ListNode(0)
        while l1 and l2:
            if l1.val < l2.val:
                l.next = l1
                l1 = l1.next
            else:
                l.next = l2
                l2 = l2.next
            l = l.next
        #l.next = l1 or l2
        if l1:
            l.next = l1
        elif l2:
            l.next = l2
        return root.next

 

 

参考答案：

def mergeTwoLists(self, l1, l2):
    if not l1 or not l2:
        return l1 or l2
    if l1.val < l2.val:
        l1.next = self.mergeTwoLists(l1.next, l2)
        return l1
    else:
        l2.next = self.mergeTwoLists(l1, l2.next)
        return l2