21-MergeTwoSorted.cs

# 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(not list1 and not list2): return
        if(not list1): return list2
        if(not list2): return list1

        pointer = None

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

        head = pointer

        while (list1 and list2):
            if(list1.val < list2.val): 
                pointer.next = list1
                pointer = pointer.next
                list1 = list1.next
            else: 
                pointer.next = list2
                pointer = pointer.next
                list2 = list2.next

        while(list1):
                pointer.next = list1
                pointer = pointer.next
                list1 = list1.next
        while(list2):
                pointer.next = list2
                pointer = pointer.next
                list2 = list2.next

        return head