LeetCode 21 _ 合并两个有序链表

 1 # Definition for singly-linked list.
 2 # class ListNode:
 3 #     def __init__(self, val=0, next=None):
 4 #         self.val = val
 5 #         self.next = next
 6 class Solution:
 7     def mergeTwoLists(self, l1: ListNode, l2: ListNode) -> ListNode:
 8         prehead = ListNode(-1)
 9         prev = prehead
10         while l1 != None and l2 != None:
11             if l1.val <= l2.val:
12                 prev.next = l1
13                 l1 = l1.next
14             else:
15                 prev.next =l2
16                 l2 = l2.next
17             prev = prev.next
18         if l1 is not None:
19             prev.next = l1 
20         else:
21             prev.next = l2
22         return prehead.next

 1 class ListNode:
 2     def __init__(self, val=0, next=None):
 3         self.val = val
 4         self.next = next
 5 if __name__ == ‘__main__‘:   
 6     l1 = ListNode(1)    
 7     l2 = ListNode(2)
 8     l3 = ListNode(3)
 9 
10     l1.next = l2
11     l2.next = l3
12 
13     #单链表遍历
14     while l1 != None:
15         print(l1.val)
16         l1 = l1.next

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