21. 合并两个有序链表

将两个升序链表合并为一个新的 升序 链表并返回。新链表是通过拼接给定的两个链表的所有节点组成的。

示例 1:

输入:l1 = [1,2,4], l2 = [1,3,4]
输出:[1,1,2,3,4,4]

示例 2:

输入:l1 = [], l2 = []
输出:[]

示例 3:

输入:l1 = [], l2 = [0]
输出:[0]

来源:力扣(LeetCode)
链接:https://leetcode-cn.com/problems/merge-two-sorted-lists
著作权归领扣网络所有。商业转载请联系官方授权,非商业转载请注明出处。

一解

使用双指针:

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def mergeTwoLists(self, l1: ListNode, l2: ListNode) -> ListNode:
        res = ListNode(None)
        tmp = res
        while l1 and l2:
            if l1.val > l2.val:
                tmp.next = l2
                l2 = l2.next
            else:
                tmp.next = l1
                l1 = l1.next
            tmp = tmp.next
        tmp.next = l1 if l1 else l2
        return res.next
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