Merge Two Sorted Lists - （合并有序链表）

Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.

Example:

Input: 1->2->4, 1->3->4
Output: 1->1->2->3->4->4

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution:
    def mergeTwoLists(self, l1, l2):
        """
        :type l1: ListNode
        :type l2: ListNode
        :rtype: ListNode
        """
        if l1 != None and l2 != None:
            if l1.val <= l2.val:
                cur = l1
                l1 = l1.next
            else:
                cur = l2
                l2 = l2.next
        else:
            return l1 if l1 != None else l2
        head = cur
        while l1 != None and l2 != None:
            if l1.val <= l2.val:
                cur.next = l1
                l1 = l1.next
            else:
                cur.next = l2
                l2 = l2.next
            cur = cur.next
        if l1 == None:
            cur.next = l2
        else:
            cur.next = l1
        return head