merge_two_sorted_lists.py

# Definition for singly-linked list.
# class ListNode:
# def __init__(self, val=0, next=None):
# self.val = val
# self.next = next
classSolution:
defmergeTwoLists(self, l1: ListNode, l2: ListNode) ->ListNode:

# the edge case(s): 
ifl1==None:
returnl2
ifl2==None:
returnl1

# we insert a 'dummy head' before the new list
dummy_node=ListNode(None) 
# new linked list
current_pointer=dummy_node
# current_pointer -> dummy_node 

while (l1!=None) and (l2!=None):
# case 1
ifl1.val<=l2.val:
current_pointer.next=l1
l1=l1.next
current_pointer=current_pointer.next
# current_pointer.next -> l1
# l1 -> l1.next
# current_pointer -> l1
# case 2
else:
current_pointer.next=l2
l2=l2.next
current_pointer=current_pointer.next
# current_pointer.next -> l2
# l2 -> l2.next
# current_pointer -> l2

ifl1==None:
current_pointer.next=l2
ifl2==None:
current_pointer.next=l1

returndummy_node.next