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