21. Merge Two Sorted Lists

21. Merge Two Sorted Lists

 

# 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]:
        dummy = ListNode()
        
        res = dummy
        while list1 and list2:
            v1 = list1.val
            v2 = list2.val
            if v1 < v2:
                res.next = ListNode(v1)
                res = res.next
                list1 = list1.next
            else: # v1 >= v2:
                res.next = ListNode(v2)
                res = res.next
                list2 = list2.next

        remain = list1 if list1 else list2

        # while remain:
        #     res.next = ListNode(remain.val)
        #     res = res.next
        #     remain = remain.next
        res.next = remain  # 위 while 문을 한줄로..
        
        
        return dummy.next

 

최종 코드

 

https://youtu.be/XIdigk956u0

 

# 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]:
        dummy = node = ListNode()

        while list1 and list2:
            if list1.val < list2.val:
                node.next = list1
                list1 = list1.next
            else:
                node.next = list2
                list2 = list2.next
            node = node.next

        # if list1 is None:
        #     node.next = list2
        # if list2 is None:
        #     node.next = list1
        node.next = list1 or list2

        return dummy.next

 

Time & Space Complexity

• Time complexity: O(n+m)
• Space complexity: O(1)

Where nn is the length of list1list1 and mm is the length of list2list2.