题目

输入两个递增排序的链表，合并这两个链表并使新链表中的节点仍然是递增排序的。
image.png

思路

双指针，边比较边插入新链表中。

代码

  1. # Definition for singly-linked list.
  2. # class ListNode:
  3. #     def __init__(self, x):
  4. #         self.val = x
  5. #         self.next = None
  7. class Solution:
  8.     def mergeTwoLists(self, l1: ListNode, l2: ListNode) -> ListNode:
  9.         if l1 is None:
  10.             return l2
  11.         if l2 is None:
  12.             return l1
  14.         dummy_node = ans =  ListNode(0)
  16.         # l1和l2都不为None时执行
  17.         while l1 and l2:
  18.             # print(l1.val)
  19.             if l1.val <= l2.val:
  20.                 ans.next = l1
  21.                 l1 = l1.next
  22.             else:
  23.                 ans.next = l2
  24.                 l2 = l2.next
  25.             ans = ans.next
  27.         # if l1 is None:
  28.         #     ans.next = l2
  29.         # if l2 is None:
  30.         #     ans.next = l1
  31.         ans.next = l1 if l1 else l2 # 更pythonic的代码
  33.         return dummy_node.next