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Leetcode 21 合并两个有序链表

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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。

直接写就行了。

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# 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, list1: Optional[ListNode], list2: Optional[ListNode]) -> Optional[ListNode]:
        
        if list1 is None and list2 is None:
            return None
        if list1 is None and list2 is not None:
            return list2
        if list1 is not None and list2 is None:
            return list1

        if list1.val <= list2.val:
            ans = ListNode(list1.val)
            list1 = list1.next
        else:
            ans = ListNode(list2.val)
            list2 = list2.next

        current = ans
        while list1 and list2:
            if list1.val <= list2.val:
                new_node = ListNode(list1.val)
                current.next = new_node
                list1 = list1.next
            else:
                new_node = ListNode(list2.val)
                current.next = new_node
                list2 = list2.next
                
            current = current.next
        if list1: current.next = list1
        if list2: current.next = list2
        return ans