【LeetCode】21. Merge Two Sorted Lists Python3解法

题目描述：

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.

例子：

Example:

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

思路：

分别比较两个list里面的第一个数值，小的创建一个新节点连接到新的list中。最后输出新的list。

代码：

class Solution:
    def mergeTwoLists(self, l1: ListNode, l2: ListNode) -> ListNode:
        #初始化linked list
        head = ListNode(0)
        #创建指针
        ptr = head
        while True:
            if l1 is None and l2 is None:
                break
            elif l1 is None:
                ptr.next = l2
                break
            elif l2 is None:
                ptr.next = l1
                break
            else:
                smaller = 0
                if l1.val < l2.val:
                    smaller = l1.val
                    l1 = l1.next 
                else:
                    smaller = l2.val
                    l2 = l2.next
                newNode = ListNode(smaller)  #将新的数值添加到新的节点中
                ptr.next = newNode           #将该节点连接到linked list中
                ptr = ptr.next               #移动新linked list中的指针
        return head.next