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

这个题目思路就是用dummy node，然后依次判断是l1 小还是l2小，最后当一方是None的时候将另一方加在总list的最后即可。

Code

class ListNode:    def __init__(self, x):        self.val = x        self.next = Noneclass Solution:    def mergeTwoLists(self, l1, l2):        dummy = ListNode(0)        head = dummy        while l1 and l2:            if l1.val <= l2.val:                head.next = l1                l1 = l1.next            else:                head.next = l2                l2 = l2.next            head = head.next        head.next = l1 if l1 else l2        return dummy.next