21. Merge Two Sorted Lists - LeetCode Solution

# 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: Optional[ListNode], l2: Optional[ListNode]) -> Optional[ListNode]:
        newList = ListNode(0)
        ptr1 = newList
        
        if not l1 and not l2:
            return None
        
        if not l1:
            return l2
        if not l2:
            return l1
        
        
        
        while True:
            if l1.val >= l2.val:
                ptr1.next = ListNode(l2.val)
                l2 = l2.next
            else:
                ptr1.next = ListNode(l1.val)
                l1 = l1.next
            
            ptr1 = ptr1.next
            
            if not l2:
                break
            if not l1:
                break
            
            
        while l1:
            ptr1.next = ListNode(l1.val)
            l1 = l1.next
            ptr1 = ptr1.next
            
        
        while l2:
            ptr1.next = ListNode(l2.val)
            
            ptr1 = ptr1.next
            l2 = l2.next
            
        return newList.next